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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Molecular and cellular biochemistry 190 (1999), S. 47-54 
    ISSN: 1573-4919
    Keywords: calmodulin ; yeast calmodulin ; Ca2+ binding ; Ca2+ binding protein ; Saccharomyces cerevisiae ; interdomain interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Calmodulin of Saccharomyces cerevisiae has different Ca2+ binding properties from other calmodulins. We previously reported that the maximum number of Ca2+ binding was 3 mol/mol and the fourth binding site was defective, which was different from 4 mol/mol for others. Their macroscopic dissociation constants suggested the cooperative three Ca2+ bindings rather than a pair of cooperative two Ca2+ bindings of ordinary calmodulin. Here we present evidence for yeast calmodulin showing the intramolecular close interaction between the N-terminal half domain and the C-terminal half domain, while the two domains of ordinary calmodulin are independent of each other. We will discuss the relationship of the shape and the shape change caused by the Ca2+ binding to the enzyme activation in yeast. The functional feature of calmodulin in yeast will also be considered, which might be different from the one of vertebrate calmodulin.
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  • 2
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    Molecular and cellular biochemistry 202 (1999), S. 109-118 
    ISSN: 1573-4919
    Keywords: NF1 mutations ; IRA1 ; Saccharomyces cerevisiae ; RAS2 ; GAP activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The 2818 amino acids of neurofibromin, the product of the human NF1 gene, include a 230 amino acid Ras-GAP related domain (GRD). Functions which may be associated with the rest of the protein remain unknown. However, many NF1 mutations in neurofibromatosis 1 patients are found downstream of the GRD, suggesting that the C-terminal region of the protein is also functionally important. Since the C-terminal region of neurofibromin encompassing these mutations is homologous with the corresponding regions in the two Saccharomyces cerevisiae Ras-GAPs, Ira1p and Ira2p, we chose yeast as a model system for functional exploration of this region (Ira-C region). Three missense mutations that affect the Ira-C region of NF1 were used as a model for the mutagenesis of IRA1. The yeast phenotypes of heat shock sensitivity, iodine staining, sporulation efficiency, pseudohyphae formation, and GAP activity were scored. Even though none of the mutations directly affected the Ira1p-GRD, mutations at two of the three sites resulted in a decrease in the GAP activity present in ira1 cells. The third mutation appeared to disassociate the phenotypes of sporulation ability and GAP activity. This and other evidence suggest an effector function for Ira1p.
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  • 3
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    Molecular and cellular biochemistry 201 (1999), S. 17-24 
    ISSN: 1573-4919
    Keywords: Saccharomyces cerevisiae ; atomic force microscope ; bioscope ; organic synthesis ; molecular biology ; oxidative stress ; pore enlargement ; cell wall ; baker's yeast ; biotechnology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract We imaged pores on the surface of the cell wall of three different industrial strains of Saccharomyces cerevisiae using atomic force microscopy. The pores could be enlarged using 10 mM diamide, an SH residue oxidant that attacks surface proteins. We found that two strains showed signs of oxidative damage via changes in density and diameter of the surface pores. We found that the German strain was resistant to diamide induced oxidative damage, even when the concentration of the oxidant was increased to 50 mM. The normal pore size found on the cell walls of American strains had diameters of about 200nm. Under conditions of oxidative stress the diameters changed to 400nm. This method may prove to be a useful rapid screening process (45-60 min) to determine which strains are oxidative resistant, as well as being able to screen for groups of yeast that are sensitive to oxidative stress. This rapid screening tool may have direct applications in molecular biology (transference of the genes to inside of living cells) and biotechnology (biotransformations reactions to produce chiral synthons in organic chemistry.
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  • 4
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    Mycopathologia 142 (1998), S. 67-70 
    ISSN: 1573-0832
    Keywords: l-glutamine ; fructose-6-phosphate amidotransferase ; Candida albicans ; fungi ; Saccharomyces cerevisiae ; Schizosaccharomyces pombe ; systemic mycoses chemotherapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The 3' part of the glucosamine-6-phosphate synthase gene from Histoplasma capsulatum was PCR amplified using degenerate primers designed from the known glucosamine-6-phosphate synthase gene sequences, cloned and sequenced. The computer analysis of the 676 bp sequence revealed the presence of two introns. The identities of the deduced amino acid sequence to the corresponding Saccharomyces cerevisiae and Candida albicans fragment are 65 and 63.8%, respectively.
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  • 5
    ISSN: 1423-0127
    Keywords: Acquired immunodeficiency syndrome ; Human immunodeficiency virus ; Nef protein ; Myristylation ; Membrane permeabilisation ; Saccharomyces cerevisiae ; Yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The human immunodeficiency virus type 1 (HIV-1) Nef protein is essential for AIDS pathogenesis, but its function remains highly controversial. During stresses such as growth in the presence of copper or at elevated temperature, myristylated Nef is released from yeast cells and, after extended culture in stationary phase, it accumulates in the supernatant as a dense membranous material that can be centrifuged into a discrete layer above the cell pellet. This material is unique to Nef-producing cells and represents a convenient source of Nef that may have application in further biological studies. Within the yeast cell, electron microscopic examination shows that Nef localises in novel, membrane-bound bodies. These data support the evidence for a role of Nef in membrane perturbation and suggest that there may be a similar localisation for myristylated Nef in HIV-1 infected cells.
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  • 6
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    Molecular and cellular biochemistry 184 (1998), S. 67-79 
    ISSN: 1573-4919
    Keywords: Saccharomyces cerevisiae ; spheroplast ; permeabilization ; mitochondria ; oxidative phosphorylation ; porin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract In this work, we first compared yeast mitochondrial oxidative metabolism at different levels of organization: whole cells (C), spheroplasts (S), permeabilized spheroplasts (PS) or isolated mitochondria (M). At present, S are more suitable for use than C for biochemical techniques such as fast extraction of metabolises and permeabilization. We show here that respiratory rates of S with various substrates are similar to C, which demonstrate that they are adapted to yeast bioenergetic studies. It appeared from ethanol metabolism ± NAD++ or NADH respiratory rates on PS that ethanol metabolism was largely cytosolic; moreover, the activity of NADH dehydrogenase was lesser in the case of PS than in S. By comparing PS and M, the biggest difference concerned the respiratory rates of pyruvate and pyruvate-malate, which were much lower for M. Thus mitochondria preparation caused an unidentified loss involved directly in pyruvate metabolism. When the respiratory rate was lowered as a consequence of a high kinetic control of oxidative activity upstream from the respiratory chain, a similar correlation between the increase in ATP/O and decrease in respiratory rate was observed. So, the intrinsic uncoupling of proton pumps is not a particularity of M. Secondly, we demonstrate the existence of a mechanism of retarded diffusion in yeast similar to that already observed in permeabilized mammalian cells for ADP. Such a mechanism also occurs in yeast for several respiratory substrates: the K0.5 for each substrate toward the respiration rate in PS always exceeds that for M. It is proposed that such a discrepancy is due to a restriction of metabolite movement across the outer mitochondrial membrane in permeabilized cells, i.e. regulation of the substrate permeability through porin channels. In the porin-deficient yeast mutant, the K0.5 for NADH is not significantly different in either M or PS and is comparable to that of the parent strain PS. This result confirms that this retarded diffusion is essentially due to the opening-closing of the porin channel.
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  • 7
    ISSN: 1573-4919
    Keywords: Saccharomyces cerevisiae ; NAD(P)H ; calcium ions ; cells immobilization ; oxygen consumption ; biotransformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The biochemical behaviour of four commercial strains of Saccharomyces cerevisiae was studied in the presence of calcium ions, acrylamide and bisacrylamide. Calcium ions at a concentration of 300 µM induced an increase of NAD(P)+ reduction in commercial Turkish and American strains, while in Chilean and Brazilian commercial strains, it diminished NAD(P)+ reduction. On the other hand, polyacrylamide monomers (acrylamide and bisacrylamide) induced a decrease of NAD(P)+ reduction in all strains studied in this paper. When membrane potential (ΔΨ) and oxygen consumption were measured in the presence of polyacrylamide monomers, a decrease of both was observed in all strains studied.
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  • 8
    ISSN: 1573-4919
    Keywords: Saccharomyces cerevisiae ; microorganisms ; dehydrogenases ; acetoacetate ; molecular modelling ; enantiomeric excess ; biotransformation ; baker's yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract This method gives a general ideal how to use crystallographic information of enzymes to understand reactions catalyzed by these biocatalysts, commonly used by biochemists to produce chiral products. The interactions of three acetoacetic esters with the enzymes L-lactate dehydrogenase and alcohol dehydrogenase were studied through molecular modelling computer program. These artificial substrates have been widely used to produce chiral synthons. Through this methodology it was possible to understand the conformational specificity of these enzymes with respect to the products and how these enzymes can be inhibited by modifying the structures of the artificial substrates. Also, it was possible to predict whether some type of artificial substrate will suffer reduction by cells that contain these dehydrogenases and what kind of configuration (R or S) the final product will have.
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  • 9
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    Molecular and cellular biochemistry 169 (1997), S. 95-106 
    ISSN: 1573-4919
    Keywords: Saccharomyces cerevisiae ; N-glycosylation ; dolichol pathway ; ALG7 ; post-transcriptional regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The yeast ALG7 gene functions by initiating the synthesis of the dolichol-linked oligosaccharide precursor and plays an important role in the control of protein N-glycosylation. The levels of ALG7 multiple transcripts are modulated by the physiological status of the cell and environmental cues, and deregulation of their abundance is deleterious to several cellular functions. Since ALG7 mRNAs are unstable, we investigated the role of these transcripts' half-lives in determining their steady-state levels. Using a temperature-sensitive RNA polymerase II mutant, we demonstrate that increased stability was the primary determinant of higher ALG7 mRNA abundance in response to glucose limitation or treatment with tunicamycin. In contrast, at the G1/G0 transition point, changes in the decay rates were inversely related to ALG7 transcript accumulation: the decreased abundance of ALG7 mRNAs following exit from the mitotic cycle was associated with lengthening of the decay rates, while their increased accumulation after growth stimulation correlated with decreased stability. This suggests that, depending on the circumstance, mRNA half-lives can either directly determine the level of ALG7 transcript accumulation or oppose regulatory changes at other control levels.
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  • 10
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    Cellular and molecular life sciences 52 (1996), S. 1130-1135 
    ISSN: 1420-9071
    Keywords: Saccharomyces cerevisiae ; mitochondria ; mRNA-specific translational activation ; synthetic genes ; gene regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Mitochondrial gene expression in yeast,Saccharomyces cerevisiae, depends on translational activation of individual mRNAs by distinct proteins encoded in the nucleus. These nuclearly coded mRNA-specific translational activators are bound to the inner membrane and function to mediate the interaction between mRNAs and mitochondrial ribosomes. This complex system, found to date only in organelles, appears to be an adaptation for targeting the synthesis of mitochondrially coded integral membrane proteins to the membrane. In addition, mRNA-specific translational activation is a rate-limiting step used to modulate expression of at least one mitochondrial gene in response to environmental conditions. Direct study of mitochondrial gene regulation and the targeting of mitochondrially coded proteins in vivo will now be possible using synthetic genes inserted into mtDNA that encode soluble reporter/passenger proteins.
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  • 11
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    Cellular and molecular life sciences 52 (1996), S. 1033-1041 
    ISSN: 1420-9071
    Keywords: Ubiquitin ; yeast ; Saccharomyces cerevisiae ; Dictyostelium discoideum ; cytoskeleton ; mutants ; endocytosis ; actin ; myosin ; calmodulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Endocytosis is a general term that is used to describe the internalization of external and plasma membrane molecules into the cell interior. In fact, several different mechanisms exist for the internalization step of this process. In this review we emphasize the work on the actin-dependent pathways, in particular in the yeastSaccharomyces cerevisiae, because several components of the molecular machinery are identified. In this yeast, the analysis of endocytosis in various mutants reveals a requirement for actin, calmodulin, a type I myosin, as well as a number of other proteins that affect actin dynamics. Some of these proteins have homology to proteins in animal cells that are believed to be involved in endocytosis. In addition, the demonstration that ubiquitination of some cell surface molecules is required for their efficient internalization is described. We compare the actin, myosin and ubiquitin requirements for endocytosis with recent results found studying these processes usingDictyostelium discoideum and animal cells.
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  • 12
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    Cellular and molecular life sciences 52 (1996), S. 1111-1116 
    ISSN: 1420-9071
    Keywords: Mitochondria ; mitochondrial inheritance ; cytoskeleton ; Saccharomyces cerevisiae ; Schizosaccharomyces pombe ; membrane proteins ; organelle movement ; mitochondrial morphology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Mechanisms mediating the inheritance of mitochondria are poorly understood, but recent studies with the yeastsSaccharomyces cerevisiae andSchizosaccharomyces pombe have begun to identify components that facilitate this essential process. These components have been identified through the analysis of conditional yeast mutants that display aberrant mitochondrial distribution at restrictive conditions. The analysis of these mutants has uncovered several novel proteins that are localized either to cytoskeletal structures or to the mitochondria themselves. Many mitochondrial inheritance mutants also show altered mitochondrial morphology and defects in maintenance of the mitochondrial genome. Although some inheritance components and mechanisms appear to function specifically in certain types of cells, other conserved proteins are likely to mediate mitochondrial behavior in all eukaryotic cells.
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  • 13
    ISSN: 1420-9071
    Keywords: Saccharomyces cerevisiae ; mitochondrial ribosomes ; peptidyl transferase ; Varl ribosomal protein ; gene relocation ; posttranscriptional rRNA modification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Mitochondria posses their own ribosomes responsible for the synthesis of a small number of proteins encoded by the mitochondrial genome. In yeast,Saccharomyces cerevisiae, the two ribosomal RNAs and a single ribosomal protein, Varl, are products of mitochondrial genes, and the remaining approximately 80 ribosomal proteins are encoded in the nucleus. The mitochondrial translation system is dispensable in yeast, providing an excellent experimental model for the molecular genetic analysis of the fundamental properties of ribosomes in general as well as adaptations required for the specialized role of ribosomes in mitochondria. Recent studies of the peptidyl transferase center, one of the most highly conserved functional centers of the ribosome, and the Varl protein, an unusual yet essential protein in the small ribosomal subunit, have provided new insight into conserved and divergent features of the mitochondrial ribosome.
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  • 14
    ISSN: 1573-4919
    Keywords: osmotic stress ; Saccharomyces cerevisiae ; glycerol ; K+/Na+ ions ; osmoregulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The intracellular level of Na+ and K+ of S. cerevisiae strain AB1375 revealed that under KCl as well as sorbitol stress, the cationic level was comparable to the level under no stress conditions. On the other hand, there was a sharp drop in the intracellular K+ content and increase in the Na+ content on addition of NaCl to the medium. However, the total cationic level was close to that under control conditions. In addition to changes in the cationic level, an enhanced production and accumulation of glycerol were also observed under osmotic stress. A regulatory mechanism co-ordinating the intracellular concentration of glycerol as well as Na+, K+ content under osmotic stress conditions has been proposed.
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  • 15
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    Molecular and cellular biochemistry 124 (1993), S. 131-140 
    ISSN: 1573-4919
    Keywords: Schizosaccharomyces pombe ; Saccharomyces cerevisiae ; H+-ATPase ; intracellular pH ; carboxy-seminaphthorhodafluor-1
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract We examined cytoplasmic pH regulation inSchizosaccharomyces pombe andSaccharomyces cerevisiae using pH-sensitive fluorescent dyes. Of several different fluorescent compounds tested, carboxy-seminaphthorhodafluor-1 (C.SNARF-1) was the most effective. Leakage of C.SNARF-1 fromS. pombe was much slower than leakage fromC. cerevisiae. Using the pH-dependent fluorescence of C.SNARF-1 we showed that at an external pH of 7, mean resting internal pH was 7.0 forS. pombe and 6.6 forS. cerevisiae. We found that internal pH inS. pombe was maintained over a much narrower range in response to changes in external pH, especially at acidic pH. The addition of external glucose caused an intracellular alkalinization in both species, although the effect was much greater inS. cerevisiae than inS. pombe. The plasma membrane H+-ATPase inhibitor diethylstilbestrol reduced both the rate and extent of alkalinisation, with an IC50 of approximately 35 μM in both species. Amiloride also inhibited internal alkalinisation with IC50's of 745 μM forS. cerevisiae and 490 μM forS. pombe.
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  • 16
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    Cellular and molecular life sciences 48 (1992), S. 1162-1164 
    ISSN: 1420-9071
    Keywords: Polygodial ; warburganal ; antifungal activity ; Candida albicans ; Saccharomyces cerevisiae ; Pityrosporum ovale ; enhancing effect ; antioxidants ; vitamin C ; BHA ; anethole
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The antifungal activity of two drimane sesquiterpene dialdehydes, polygodial (1) and warburganal (2), alone and in combination with several other substances, was examined against three fungi,Candida albicans, Saccharomyces cerevisiae andPityrosporum ovale employing a broth dilution method. Anethole significantly synergized the activity of the two sesquiterpenoids againstC. albicans andS. cerevisiae however, it had only an, additive effect againstP. ovale. By contrast, two antioxidants, ascorbic acid (vitamin C) and BHA (butylated hydroxyanisole), noticeably enhanced the activity of the sesquiterpenoids againstP. ovale, but had no, effect againstC. albicans andS. cerevisiae.
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  • 17
    ISSN: 1573-4919
    Keywords: glutathione reductase ; Saccharomyces cerevisiae ; redox interconversion ; metals ; cell-free extracts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Redox inactivation of glutathione reductase involves metal cations, since chelators protected against NADPH-inactivation, 3 µM EDTA or 10 µM DETAPAC yielding full protection. Ag+, Zn2+ and Cd2+ potentiated the redox inactivation promoted by NADPH alone, while Cr3+, Fe2+, Fe3+, Cu+, and Cu2+ protected the enzyme. The Zn2+ and Cd2+ effect was time-dependent, unlike conventional inhibition. Glutathione reductase interconversion did not require dioxygen, excluding participation of active oxygen species produced by NADPH and metal cations. One Zn2+ ion was required per enzyme subunit to yield full NADPH-inactivation, the enzyme being reactivated by EDTA. Redox inactivation of glutathione reductase could arise from the blocking of the dithiol formed at the active site of the reduced enzyme by metal cations, like Zn2+ or Cd2+. The glutathione reductase activity of yeast cell-free extracts was rapidly inactivated by low NADPH or moderate NADH concentrations; NADP+ also promoted rapid inactivation in fresh extracts, probably after reduction to NADPH. Full inactivation was obtained in cell-free extracts incubated with glucose-6-phosphate or 6-phosphogluconate; the inactivating efficiency of several oxidizable substrates was directly proportional to the specific activities of the corresponding dehydrogenases, confirming that redox inactivation derives from NADPH formed in vitro.
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  • 18
    ISSN: 1573-0832
    Keywords: Nystatin ; amphotericin B ; amphotericin B methyl ester ; polyene antibiotics ; yeast ; Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Saccharomyces cerevisiae was cultured under anaerobiosis in semi-complete medium to which either palmitoleic or oleic acid was added. Cells were grown at 20 °C or 30 °C. The levels of total lipids, total sterols, and phospholipids were higher in cells grown at 20 °C than at 30 °C. The effects of nystatin (NYS), amphotericin B (AMB), and amphotericin B methyl ester (AME) were evaluated by determining cell viability and liberation of intracellular compounds. The loss of cell viability is higher in the first 30 minutes of incubation with the drugs and is the same regardless of the type of cells obtained. Low molecular weight compounds and ions such as K+ are liberated a few minutes after incubation with the drugs whereas proteins and substances absorbing at 260 nm are liberated later. Phosphate liberation comes after K+ and before compounds of higher molecular weights.
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  • 19
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    Cellular and molecular life sciences 46 (1990), S. 193-200 
    ISSN: 1420-9071
    Keywords: Saccharomyces cerevisiae ; protein toxin ; yeast toxin precursor ; protease processing ; lectin ; (1→6)-β-D-glucan ; receptor ; resistant mutants ; spheroplasts ; ion-permeable channels ; site-directed mutagenesis ; toxin functional domains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The K1 killer toxin ofSaccharomyces cerevisiae is a secreted, virally-coded protein lethal to sensitive yeasts. Killer yeasts are immune to the toxin they produce. This killer system has been extensively examined from genetic and molecular perspectives. Here we review the biology of killer yeasts, and examine the synthesis and action of the protein toxin and the immunity component. We summarise the structure of the toxin precursor gene and its protein products, outline the proteolytic processing of the toxin subunits from the precursor, and their passage through the yeast secretory pathway. We then discuss the mode of action of the toxin, its lectin-like interaction with a cell wall glucan, and its probable role in forming channels in the yeast plasma membrane. In addition we describe models of how a toxin precursor species functions as the immunity component, probably by interfering with channel formation. We conclude with a review of the functional domains of the toxin structural gene as determined by site-directed mutagenesis. This work has identified regions associated with glucan binding, toxin activity, and immunity.
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  • 20
    ISSN: 1573-4919
    Keywords: bovine heart fatty acid-binding protein ; H-FABPc ; heterologous gene expression ; Saccharomyces cerevisiae ; GALIO promoter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary The unicellular eukaryotic microorganism, Saccharomyces cerevisiae, transformed with a plasmid containing a cDNA fragment encoding bovine heart fatty acid-binding protein (H-FABP) under the control of the inducible yeast GAL10 promoter, expressed FABP during growth on galactose. The maximum level of immunoreactive FABP, identical in size to native protein as judged from SDS-polyacrylamide gel electrophoresis, was reached after approximately 16 hours of induction. Analysis of particulate and soluble subcellular fractions showed that FABP was exclusively associated with the cytosol. FABP expressed in yeast cells was functional as was demonstrated by its capacity to bind 14C-oleic acid in an in vitro assay. Growth of the transformants on galactose as the carbon source was significantly retarded at 37°C. Whereas the fatty acid pattern of total lipids was not altered in transformed cells, desaturation of exogenously added 14C-palmitic acid was significantly reduced both at 30 and 37°C. The lowest percentage of radioactively labeled unsaturated fatty acids was found in the phospholipid fraction.
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  • 21
    ISSN: 1420-9071
    Keywords: Saccharomyces cerevisiae ; growth conditions ; kinaseless mutant ; plasma membrane vesicles ; glucose transport ; kinetics and computer simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In this study experimental data on the kinetic parameters investigated by other authors1–5, 11 together with own data on plasma membrane vesicles, have been subjected to a computer simulation based on the equations describing facilitated diffusion. The simulation led to an ideal fit describing the above data. From this it can be concluded that glucose is transported by facilitated diffusion, and not by active transport as was postulated by Van Steveninck14, 15. The simulation method also demonstrates that the fast sampling technique used by these authors1–5,11 underestimates the fluxes. Thus, the parameters given do not contribute to the understanding of glucose transport under different metabolic conditions. The K value of plasma membrane vesicles prepared from glucose-repressed cells is around 7 mM. Derepression, particularly by galactose, causes a highly significant increase in affinity as shown by a decrease in the K value to 2 mM. The highest affinity was measured in a triple kinaseless mutant grown on glycerol with a K value of 1 mM. If seems, therefore, that the kinetic parameters derived from initial uptake rates of glucose in intact cells1–5,11 using single flux analysis, such as Eadie-Hofstee- or Lineweaver-Burk-plots, are in error.
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  • 22
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    Cellular and molecular life sciences 43 (1987), S. 886-888 
    ISSN: 1420-9071
    Keywords: Saccharomyces cerevisiae ; trichothecenes ; mycotoxins ; vitamins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Several trichothecene mycotoxins were shown to inhibit the growth ofSaccharomyces cerevisiae. This effect was most pronounced with the macrocyclic trichothecenes, especially verrucarin A. Much less growth inhibition was observed with T-2 toxin. Verrucarol, diacetoxyscirpenol, acetyl T-2 toxin, HT-2 toxin, T-2 tetraol and neosolaniol were inactive at a concentration of 75 μg of toxin per disc. Incubation ofS. cerevisiae with verrucarin A together with vitamins resulted in a decrease in toxicity. Pyridoxine-HCl, Ca-pantothenate, thiamine-HCl and α-tocopheryl acetate were amongst the most potent of the vitamins tested which reversed growth inhibition, overcoming the inhibitory potential of the toxins.
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  • 23
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    Cellular and molecular life sciences 43 (1987), S. 888-890 
    ISSN: 1420-9071
    Keywords: Thiaminase ; thiamine ; thiamine antagonist ; Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary It was found that cell-free extracts ofSaccharomyces cerevisiae contain thiaminase II which hydrolyzes thiamine and thiamine analogs. The possible involvement of this enzyme and thiamine-synthesizing enzymes in thiamine production from thiamine antagonists is discussed.
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  • 24
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    Cellular and molecular life sciences 40 (1984), S. 1159-1161 
    ISSN: 1420-9071
    Keywords: Saccharomyces cerevisiae ; 5-trifluoromethyl-6-àzauracil ; yeast cell cultures ; cell division ; inhibition of
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Cell division, as studied in asynchronous cultures of yeast cells, is sensitive to 5-trifluoromethyl-6-azauracil (F3CAzU). Under defined conditions (10 mmoles l−1 F3CAzU) this compound blocks immediately and completely the process of cell division. Using synchronized cells, the time-point at which division process of yeast cell can be inhibited by F3CAzU has been determined. The inhibitor effect of this compound is completely reversed by thymine, thymidine and uracil.
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  • 25
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    European journal of nutrition 22 (1983), S. 205-212 
    ISSN: 1436-6215
    Keywords: Schwermetallwirkung ; Malatdehydrogenase ; Glutamatdehydrogenase ; Glycerinaldehyd-3-phosphatdehydrogenase ; Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Medicine
    Description / Table of Contents: Summary The difference between cadmium, zinc, lead, and mercury in regard of their effects on the activity of the enzymes tested is very slight. Concentrations higher than 10−5 M reduce significantly the activity of the enzymes, and concentrations of approximately 10−3 M inhibit it completely. An increase of the activity cannot be detected. The addition of combinations of cadmium, zinc, and lead results in a summing up of the toxic effects, whereas the interaction between mercury and the other three heavy metals shows a cumulative effect, which is appointed nearly completely by the heavy metal more toxic. The findings suggest that under in-vitro conditions there exists a direct interaction between the heavy metals and the enzymes.
    Notes: Zusammenfassung Die vier Schwermetalle Cadmium, Zink, Blei und Quecksilber unterscheiden sich in ihrer Wirkung auf die Aktivität der untersuchten Enzyme nur sehr wenig. Konzentrationen über 10−5 M vermindern die Enzymaktivität signifikant, und Konzentrationen von etwa 10−3 M unterbinden sie völlig. Eine Steigerung der Enzymaktivität läßt sich nicht feststellen. Die Zugabe von Cadmium-, Zink- und Bleikombinationen führt zu einer Addition der toxischen Effekte, während bei der Interaktion zwischen Quecksilber und den anderen drei Schwermetallen die Gesamtwirkung fast ausschließlich durch das stärker hemmende Schwermetall allein bestimmt wird. Die erhaltenen Ergebnisse lassen vermuten, daß es unter Invitro-Bedingungen zu einer direkten Wechselwirkung zwischen den Schwermetallen und den Enzymen kommt.
    Type of Medium: Electronic Resource
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