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  • 1
    Electronic Resource
    Electronic Resource
    The 2-oxoglutarate/malate translocator of chloroplast envelope membranes: molecular cloning of a transporter containing a 12-helix motif and expression of the functional protein in yeast cells (1995)
    s.l. : American Chemical Society
    Biochemistry 34 (1995), S. 2621-2627 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00008a028
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  • 2
    Electronic Resource
    Electronic Resource
    Functional genomics of phosphate antiport systems of plastids (2003)
    Oxford, UK : Munksgaard International Publishers
    Physiologia plantarum 118 (2003), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Plant cells require a co-ordination of metabolism between their major compartments, the plastids and the cytosol, in particular as certain metabolic pathways are confined to either compartments. The inner envelope membrane of the plastids forms the major barrier for metabolite exchange and is the site for numerous transport proteins, which selectively catalyse metabolite exchanges characteristic for green and/or non-green tissues. This report is focused on the molecular biology, evolution and physiological function of the family of phosphate translocators (PT) from plastids. Until now, four distinct subfamilies have been identified and characterized, which all share inorganic phosphate as common substrate, but have different spectra of counter exchange substrates to fulfil the metabolic needs of individual cells and tissues. The PTs are named after their main transported substrate, triose phosphate (TPT), phosphoenolpyruvate (PPT), glucose 6-phosphate (GPT) and xylulose 5-P (XPT). All PTs belong to the TPT/nucleotide sugar transporter (NST) superfamily, which includes yet uncharacterized PT homologues from plants and other eukaryotes. Transgenic plants or mutants with altered transport activity of some of the PTs have been generated or isolated. The analysis of these plant lines revealed new insights in the co-ordination and flexibility of plant metabolism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.2003.00137.x
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  • 3
    Electronic Resource
    Electronic Resource
    The major chloroplast envelope polypeptide is the phosphate translocator and not the protein import receptor (1991)
    [s.l.] : Nature Publishing Group
    Nature 353 (1991), S. 364-367 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Polypeptide profiles of envelope membranes from spinach and pea chloroplasts are shown in Fig. la. The main poly-peptides of these membranes have different apparent relative molecular masses (Mr) of 29,000 (29 K; E29 (spinach); lane 1), and 30K (E30 (pea); lane 2). When the precursor proteins are ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/353364a0
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of antisense repression of the chloroplast triose-phosphate translocator on photosynthetic metabolism in transgenic potato plants (1994)
    Springer
    Planta 193 (1994), S. 174-180 
    Details
    ISSN: 1432-2048
    Keywords: Antisense repression ; Photosynthesis ; Solanum ; Starch synthesis ; Triose phosphate translocator
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The introduction of an antisense DNA into transgenic potato (Solanum tuberosum L.) plants decreased the expression of the chloroplast triose-phosphate translocator and lowered its activity by 20–30%. With plants propagated from tubers, the effect of the transformation on photosynthetic metabolism was analysed by measuring photosynthesis, the formation of leaf starch, and the total and subcellular metabolite contents in leaves. Although the transformants, in contrast to those propagated from cell cultures, did not differ from the wild-type plants in respect to rates of photosynthesis, plant appearance, growth and tuber production, their photosynthetic metabolism was found to be severely affected. The results show that the decrease in activity of the triose-phosphate translocator in the transformants caused a fourfold increase in the level of 3-phosphoglycerate and a corresponding decrease in inorganic phosphate in the stromal compartment, resulting in a large increase in the synthesis of starch. Whereas during a 12-h day period wild-type plants deposited 43% of their CO2 assimilate into starch, this value rose to 61–89% in the transformants. In contrast to the wild-type plants, where the rate of assimilate export from the leaves during the night period was about 75% of that during the day, the export rate from leaves of transformants appeared to be much higher during the night than during the day. As the mobilisation of starch occurs in part hydrolytically, resulting in the formation of glucose, the triose-phosphate translocator loses its exclusive function in the export of carbohydrates from the chloroplasts when the photoassimilates are temporarily deposited as starch. It appears that by directing the CO2 assimilates mainly into starch, the transformants compensate for the deficiency in triose-phosphate translocator activity in such a way that the productivity of the plants is not affected by the transformation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192527
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  • 5
    Electronic Resource
    Electronic Resource
    Compensation of decreased triose phosphate/phosphate translocator activity by accelerated starch turnover and glucose transport in transgenic tobacco (1998)
    Springer
    Planta 204 (1998), S. 366-376 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Antisense repression ; Glucose translocator ; Nicotiana ; Starch mobilisation ; Triose phosphate/phosphate translocator
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Tobacco (Nicotiana tabacum L.) plants were transformed with an antisense construct of the chloroplast triose phosphate/phosphate translocator (TPT). Three transformant lines of the T4 progeny, which showed a large decrease in the transcript level of the TPT were used for further biochemical and physiological characterisation. In all antisense lines tested, TPT transport activity was diminished by 50–70% compared with the wild type (WT). Despite this high reduction in the transport capacity, αTPT plants lacked any visible phenotype. Hexokinase and α-amylase activities were increased in αTPT plants compared with the WT, whereas activities of ribulose-1,5-bisphosphate carboxylase/oxygenase and ADP-glucose pyrophosphorylase (AGPase) were not affected. At the end of a 14-h light period, leaf starch contents in αTPT lines were similar to those of the WT and controls, indicating that a decrease in the TPT had no effect on starch accumulation. Sucrose contents were diminished by more than 50% in αTPT lines compared with control plants. The time course of starch accumulation revealed a transient increase in the starch content in a selected αTPT line after 6 h in the light, followed by a decrease towards the end of the light period. Labelling with 14C indicated that during the dark and light (late afternoon) periods starch is mobilised at higher rates in αTPT lines than in the controls. Glucose/fructose ratios at the end of the dark period were increased from 1.2 in control plants to 2 in αTPT lines indicating increased amylolytic starch degradation. Initial rates of [14C] glucose transport in isolated chloroplasts were increased by a factor of 2–3 in αTPT plants compared with the WT. Rates of CO2 assimilation were substantially diminished in the αTPT lines in high CO2 and low O2, but remained unaffected in ambient CO2. The rate of photosynthetic electron transport during the induction of photosynthesis in saturating CO2 exhibited pronounced oscillations only in WT and control plants. Oscillations were less pronounced in αTPT plants, indicating that phosphate limitation of photosynthesis is lowered in αTPT plants compared with the WT. It is proposed that photoassimilates are more readily directed into starch biosynthesis in αTPT plants. This is supported by determinations of 3-phosphoglycerate levels (an activator of AGPase) during the transition from dark to light in high CO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050268
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  • 6
    Electronic Resource
    Electronic Resource
    Molecular cloning and structural analysis of the phosphate translocator from pea chloroplasts and its comparison to the spinach phosphate translocator (1991)
    Springer
    Planta 183 (1991), S. 451-461 
    Details
    ISSN: 1432-2048
    Keywords: Amphiphilic α-helix ; cDNA sequence ; Chloroplast protein import ; Phosphate translocator Pisum (phosphate translocator) ; Spinacia (phosphate translocation) ; Transit peptide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Using an 5′-AvaII fragment of the spinach (Spinacia oleracea L.) phosphate translocator cDNA as a probe for a hybridization screening of a pea (Pisum sativum L.) cDNA library we have cloned and sequenced a cDNA clone coding for the phosphate translocator precursor protein from pea chloroplasts. The full-length cDNA clone comprises 42 base pairs (bp) at the 5′-non-coding region, a 1206-bp coding region corresponding to a polypeptide of 402 amino-acid residues (relative molecular mass 43 671) and 244 bp at the non-coding 3′-region. Determination of the N-terminal sequence of the phosphate translocator from both pea and spinach chloroplasts revealed that the transit peptides consist of 72 and 80 amino-acid residues, respectively. These transit peptides are different from those of other chloroplastic transit peptides in that they both contain an amphiphilic α-helix which is located either in close proximity to the processing site in pea or at the N-terminus in spinach. The mature proteins from pea and spinach both contain about 87% identical amino-acid residues and about seven putative membrane-spanning α-helices. Some of these α-helices have an amphiphilic character and might serve to form a hydrophilic translocation channel through the membrane. The in-vitro synthesized pea precursor protein is directed to the chloroplast and inserted into the chloroplast envelope membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197745
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  • 7
    Electronic Resource
    Electronic Resource
    A rapid method for measuring organelle-specific substrate transport in homogenates from plant tissues (1994)
    Springer
    Planta 194 (1994), S. 181-185 
    Details
    ISSN: 1432-2048
    Keywords: Metabolite transport ; Plant cell membranes ; Reconstitution (membranes)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A rapid method is described for measuring organelle-specific metabolite transport systems in crude homogenates from plants. The tissues were homogenized in liquid nitrogen, extracted with buffer and reconstituted into artificial membranes. The method allowed demonstration of the known different substrate specificities of chloroplast triose phosphate/phosphate translocators from C3- and C4-plants, of the triose phosphate/phosphate translocator from non-green tissue, and of the dicarboxylate translocator. It thus by-passes the necessity to isolate intact plant organelles and, in addition, only a low amount of tissue material is required for transport measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00196386
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  • 8
    Electronic Resource
    Electronic Resource
    A rapid method for measuring organelle-specific substrate transport in homogenates from plant tissues (1994)
    Springer
    Planta 194 (1994), S. 181-185 
    Details
    ISSN: 1432-2048
    Keywords: Metabolite transport ; Plant cell membranes ; Reconstitution (membranes)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A rapid method is described for measuring organelle-specific metabolite transport systems in crude homogenates from plants. The tissues were homogenized in liquid nitrogen, extracted with buffer and reconstituted into artificial membranes. The method allowed demonstration of the known different substrate specificities of chloroplast triose phosphate/phosphate translocators from C3- and C4-plants, of the triose phosphate/phosphate translocator from non-green tissue, and of the dicarboxylate translocator. It thus by-passes the necessity to isolate intact plant organelles and, in addition, only a low amount of tissue material is required for transport measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01101676
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  • 9
    Electronic Resource
    Electronic Resource
    Control of carbon partitioning and photosynthesis by the triose phosphate/phosphate translocator in transgenic tobacco plants (Nicotiana tabacum L.). I. Comparative physiological analysis of tobacco plants with antisense repression and overexpression of the triose phosphate/phosphate translocator (2000)
    Springer
    Planta 210 (2000), S. 371-382 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Antisense repression/overexpression – Car-bohydrate metabolism – Carbon partitioning –Flaveria– Nicotiana (transgenic) – Triose phosphate/phosphate translocator – Starch mobilisation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract.  The physiological properties of transgenic tobacco plants (Nicotiana tabacum L.) with decreased or increased transport capacities of the chloroplast triose phosphate/phosphate translocator (TPT) were compared in order to investigate the extent to which the TPT controls metabolic fluxes in wild-type tobacco. For this purpose, tobacco lines with an antisense repression of the endogenous TPT (αTPT) and tobacco lines overexpressing the TPT gene isolated from the C4 plant Flaveria trinervia (FtTPT) were used. The F. trinervia TPT expressed in yeast cells exhibited transport characteristics identical to the TPT from C3 plants. Neither antisense TPT plants nor FtTPT overexpressors showed a phenotype when grown in a greenhouse in air. Contents of starch and soluble sugars in upper source leaves were similar in TPT underexpressors and FtTPT overexpressors compared to the wild type at the end of the photoperiod. The FtTPT overexpressors incorporated more 14CO2 in sucrose than the wild type, indicating that the TPT limits sucrose biosynthesis in the wild type. There were only small effects on labelling of amino acids and organic acids. The mobilisation of starch was enhanced in αTPT lines but decreased in FtTPT overexpressors compared to the wild type. Enzymes involved in starch mobilisation or utilisation, such as α-amylase or hexokinase were increased in αTPT plants and, in the case of amylases, decreased in FtTPT overexpressors. Moreover, α-amylase activity exhibited a pronounced diurnal variation in αTPT lines with a maximum activity after 8 h in the light. These changes in starch hydrolytic activities were confirmed by activity staining of native gels. Activities of glucan phosphorylases were unaffected by either a decrease or an increase in TPT activity. There were also effects of TPT activities on steady-state levels of phosphorylated intermediates as well as total amino acids and malate. In air, there was no or little effect of altered TPT transport activity on either rates of photosynthetic electron transport and/or CO2 assimilation. However, in elevated CO2 (1500 μl · l−1) and low O2 (2%) the rate of CO2 assimilation was decreased in the αTPT lines and was slightly higher in FtTPT lines. This shows that the TPT limits maximum rates of photosynthesis in the wild type.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00008145
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  • 10
    Electronic Resource
    Electronic Resource
    The 24kDa outer envelope membrane protein from spinach chloroplasts: molecular cloning, in vivo expression and import pathway of a protein with unusual properties (1994)
    Springer
    Plant molecular biology 25 (1994), S. 167-177 
    Details
    ISSN: 1573-5028
    Keywords: Spinacia oleracea ; chemical cleavage ; gene expression ; polymerase chain reaction ; protein transport ; SDS-PAGE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The 24 kDa outer envelope membrane protein of spinach chloroplasts (omp24) represents a major constituent of this membrane. Sequences of tryptic and endoprotease Glu-C peptides derived from omp24 allowed the design of oligonucleotides which were used to generate a DNA fragment by polymerase chain reaction using spinach cDNA as template. This fragment served as a probe to screen a cDNA library for a full-length clone of the omp24 coding sequence. The protein predicted from the complete sequence only has 148 amino acids and a molecular mass of 16294 Da. It is an acidic protein (calculated isoelectric point 4.8) with a high content of proline residues. Expression of the coding sequence in Escherichia coli and characterization of the purified recombinant protein produced revealed that the overestimation of its molecular mass by SDS-PAGE (ca. 25 kDa) is due to its abnormal amino acid composition. Despite its rather low hydrophobicity (polarity index 49%), omp24 appears to be deeply embedded in the outer membrane. Insertion of omp24 into the membrane proceeds almost independently of surface receptors or targeting sequence but, in contrast to other known outer envelope membrane proteins, is stimulated by ATP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00023235
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