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  • Chemistry  (24)
  • Organic Chemistry  (3)
  • CoA ligase  (2)
  • 68.35  (1)
  • 2020-2021
  • 1990-1994  (27)
  • 1960-1964
  • 1
    Electronic Resource
    Electronic Resource
    Wavelength-dependent anisotropy of surface second-harmonic generation from Si(111) in the vicinity of bulk absorption (1994)
    Springer
    Applied physics 58 (1994), S. 111-115 
    Details
    ISSN: 1432-0649
    Keywords: 42.65 ; 68.35
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A wavelength-dependence study of surface second-harmonic generation from Si(111) is presented. Femtosecond laser pulses tuned from 430 nm to 710 nm were used to probe the dispersion characteristics of the nonlinear response from the surface in the vicinity of bulk absorption. Changes in the rotational symmetry and in the phase of the generated second-harmonic signal were observed. An explanation of the observed changes is given based on a simple anharmonic oscillator model [1]
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01082344
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  • 2
    Electronic Resource
    Electronic Resource
    Purification and characterization of phenylacetate-coenzyme A ligase from a denitrifying Pseudomonas sp., an enzyme involved in the anaerobic degradation of phenylacetate (1993)
    Springer
    Archives of microbiology 159 (1993), S. 554-562 
    Details
    ISSN: 1432-072X
    Keywords: Phenylacetate ; CoA ligase ; Phenylacetyl ; CoA ; Anaerobic aromatic metabolism ; Pseudomonas ; Alpha ; Oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The enzyme catalysing the first step in the anaerobic degradation pathway of phenylacetate was purified from a denitrifying Pseudomonas strain KB 740. It catalyses the reaction phenylacetate+CoA+ATP → phenylacetyl-CoA+AMP+PPi and requires Mg2+. Phenylacetate-CoA ligase (AMP forming) was found in cells grown anaerobically with phenylacetate and nitrate. Maximal specific enzyme activity was 0.048 μmol min-1 x mg-1 protein in the mid-exponential growth phase. After 640-fold purification with 18% yield, a specific activity of 24.4 μmol min-1 mg-1 protein was achieved. The enzyme is a single polypeptide with Mr of 52 ±2 kDa. The purified enzyme shows high specificity towards the aromatic inducer substrate phenylacetate and uses ATP preferentially; Mn2+ can substitute for Mg2+. The apparent K m values for phenylacetate, CoA, and ATP are 60, 150, and 290 μM, respectively. The soluble enzyme has an optimum pH of 8.5, is insensitive to oxygen, but is rather labile and requires the presence of glycerol and/or phenylacetate for stabilization. The N-terminal amino acid sequence showed no homology to other reported CoA-ligases. The expression of the enzye was studied by immunodetection. It is present in cells grown anaerobically with phenylacetate, but not with mandelate, phenylglyoxylate, benzoate; small amounts were detected in cells grown aerobically with phenylacetate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00249035
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  • 3
    Electronic Resource
    Electronic Resource
    Anaerobic oxidation of phenylacetate and 4-hydroxyphenylacetate to benzoyl-coenzyme A and CO2 in denitrifying Pseudomonas sp. (1993)
    Springer
    Archives of microbiology 159 (1993), S. 563-573 
    Details
    ISSN: 1432-072X
    Keywords: Phenylacetate ; 4-Hydroxyphenylacetate ; Phenylglyoxylate ; Alpha-Oxidation ; Pseudomonas ; Oxidoreductase ; CoA ligase ; Benzoyl-CoA ; Anaerobic aromatic metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Anaerobic degradation of (4-hydroxy)phenylacetate in denitrifying Pseudomonas sp. was investigated. Evidence is presented for α-oxidation of the coenzyme A (CoA)-activated carboxymethyl side chain, a reaction which has not been described. The C6−C2 compounds are degraded to benzoyl-CoA and furtheron to CO2 via the following intermediates: Phenylacetyl-CoA, phenylglyoxylate, benzoyl-CoA plus CO2; 4-hydroxyphenylacetyl-CoA, 4-hydroxyphenylglyoxylate, 4-hydroxybenzoyl-CoA plus CO2, benzoyl-CoA. Trace amounts of mandelate possibly derived from mandelyl-CoA were detected during phenylacetate degradation in vitro. The reactions are catalyzed by (i) phenylacetate-CoA ligase which converts phenylacetate to phenylacetyl-CoA and by a second enzyme for 4-hydroxyphenylacetate; (ii) a (4-hydroxy)-phenylacetyl-CoA dehydrogenase system which oxidizes phenylacetyl-CoA to (4-hydroxy)phenylglyoxylate plus CoA; and (iii) (4-hydroxy)phenylglyoxylate: acceptor oxidoreductase (CoA acylating) which catalyzes the oxidative decarboxylation of (4-hydroxy)phenylglyoxylate to (4-hydroxy)benzoyl-CoA and CO2. (iv) The degradation of 4-hydroxyphenylacetate in addition requires the reductive dehydroxylation of 4-hydroxybenzoyl-CoA to benzoyl-CoA, catalyzed by 4-hydroxybenzoyl-CoA reductase (dehydroxylating). The whole cell regulation of these enzyme activities supports the proposed pathway. An ionic mechanism for anaerobic α-oxidation of the CoA-activated carboxymethyl side chain is proposed. Phenylacetic acids are plant constituents and in addition are formed from a large variety of natural aromatic compounds by microorganisms; their degradation therefore plays a significant role in nature, as illustrated in the preceding paper (Mohamed and Fuchs 1993). We have investigated and purified an enzyme which catalyzes the first step in the anaerobic degradation of phenylacetate in a denitrifying Pseudomonas sp. Phenylacetate is converted to phenylacetyl-CoA by phenylacetate-CoA ligase (AMP forming). The postulated function of this enzyme is corroborated by the strict regulation of its expression. 4-Hydroxyphenylacetate appears to be similarly activated by an independent enzyme prior to further degradation. We have suggested before that phenylacetyl-CoA is anaerobically converted by α-oxidation of the side chain to phenylglyoxylate1, which is oxidatively decarboxylated to benzoyl-CoA plus CO2 (Seyfried et al. 1991; Dangel et al. 1991). 4-Hydroxyphenylacetate was proposed to be similarly oxidized to 4-hydroxybenzoyl-CoA plus CO2, followed by reductive dehydroxylation to benzoyl-CoA. The evidence was not presented in full, and the crucial α-oxidation was not demonstrated in vitro. We present here ample evidence for this pathway. A hypothetical mechanism is proposed by which the oxidation of the α-methylene group to an α-carbonyl group may occur.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00249036
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  • 4
    Electronic Resource
    Electronic Resource
    Enkephalin analogues containing β-naphthylalanine at the fourth position (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 179-196 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To examine the importance of the aromatic side chains of enkephalin on opiate activity, we report the synthesis and conformational analysis of a series of analogues related to enkephalin with β-naphthylalanine in place of phenylalanine at the fourth position. Three linear analogues (Tyr-D-Ala-Gly-(L and D)-β Nal(1)-Leu-NH2 and Tyr-D-Ala-Gly-β Nal(2)-Leu-NH2) were initially synthesized to examine the effect of the substitution on biological activity. The increased activity of these peptides at the μ-opiate receptor, compared to native Leu-enkephalin, prompted us to examine the more conformational constrained analogues, Tr-c[D-A2bu-Gly-(L and D)-β Nal(1)-Leu], incorporating a α,γ-diaminobutyric acid at the second position and cyclization to the carboxylic end of the leucine. These two cyclic analogues provide insight into the necessity for the L chirality of the aromatic residue at position 4. The Tyr-c[D-A2bu-Gly-L-β Nal(1)-Leu] analogue is highly potent and displays a slight preference for the μ receptor. The conformational analysis indicates that despite the high flexibility of the tyrosine side chain, the aromatic rings of the tyrosine and naphthylalanine are relatively distant from each other. The presence of two intramolecular hydrogen bonds help maintain the conformation of the 14-membered backbone ring that keeps the side chains directed away from each other. These findings are in agreement with our model of an extended structure required for μ selectivity and a folded form with close aromatic ring placement for δ selectivity.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290123
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  • 5
    Electronic Resource
    Electronic Resource
    Molecular-weight distributions in the thermally initiated emulsion polymerization of styrene (1991)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 405-414 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In both thermal emulsion polymerization of styrene in the temperature range 60-80 °C, and peroxodisulfate-initiated polymerization at 60 °C, weight-average to number-average molecular-weight ratios (M̄w/M̄n) approach 1,5 when potassium octadecanoate is used as emulsifier. A low activation energy for thermal initiation (≈66,0 kJ/mol) was deduced which may indicate a catalytic effect of the emulsifier during the thermal initiation process. Participation of the emulsifier is probably attributed to a transfer of one of two monomer radicals, produced thermally, to the emulsifier, with subsequent desorption to the aqueous phase, leaving one radical in the polymerization locus.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1991.021920220
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  • 6
    Electronic Resource
    Electronic Resource
    Perfluorinated anion exchange membranes: Preparation and preliminary tests of dialysis (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1407-1412 
    Details
    ISSN: 0887-624X
    Keywords: radiochemical grafting ; anion exchange membrane ; acid dialysis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using the preirradiation technique a kinetic study of the grafting of the 4-vinyl pyridine (V4P) and an aliphatic ammonium monomer (ALAM) onto the copolymer film of ethylene-tetrafluoroethylene (ETFE) has been performed. The influence of dose, temperature, and concentration of monomer, reticular agent, and inhibitor were investigated. The results are discussed on the basis of the interactions between monomer diffusibility and viscosity of the medium. The characteristics of some membranes were determined. Their applicability to the recovery of acid by dialysis is demonstrated.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300720
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  • 7
    Electronic Resource
    Electronic Resource
    Catalytic dehydrogenation of ethylbenzene to styrene in membrane reactors (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 2055-2059 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690401215
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  • 8
    Electronic Resource
    Electronic Resource
    Competitive hydrodesulfurization and hydrogenation in a monolithic reactor (1990)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 36 (1990), S. 746-752 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Competitive liquid-phase hydrodesulfurization of thiophene and hydrogenation of cyclohexene on a monolithic CoMo/γ-Al2O3 catalyst were studied. The flow pattern in the monolithic catalyst reactor was segmented gas-liquid flow (slug flow). The hydrogen pressure and the temperature were varied between 30-40 bar and 509-523 K, respectively. The experimental data are consistent with rate expressions of the Langmuir-Hinshelwood type where the reactions proceed on two different types of active sites. This kinetic model is based on hydrogenation of the thiophene ring prior to sulfur elimination.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690360511
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  • 9
    Electronic Resource
    Electronic Resource
    The electrical conductivity of cellulose HYPHAN® and its complexes (1993)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 212 (1993), S. 13-18 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die elektrische Leitfähigkeit (σ) von Cellulose-HYPHAN® und seinen Komplexen mit Cr3+, Mn2+, Mo5+ und Hg2+ wurde im Temperaturbereich 25-510°C bestimmt. Die Aktivierungsenergie wurde aus der Abhängigkeit von log σ von der reziproken Temperatur berechnet. Die Ergebnisse zeigen, daß die Leitfähigkeit mit steigender Temperatur zunimmt und dabei zwei Maxima durchläuft. Das erste Maximum läßt sich dem Wassergehalt zuordnen, während das zweite mit dem thermischen Abbau der Cellulose-Kette zusammenhängt. Die Werte der Aktivierungsenergie lassen darauf schlieäen, daß sich beim Erhitzen die Halbleitereigenschaften der Komplexe verbessern.
    Notes: The electrical conductivity, σ, of cellulose HYPHAN® and its complexes with Cr3+, Mn2+, Mo5+ or Hg2+ was measured from room temperature to 510°C. The activation energy, ΔE, of the samples was calculated from log σ against 1/T curves. The results show that the electrical conductivity increases by temperature with two maximum peaks. The first peak is attributed to the moisture content, while the second one is attributed to the thermal degradation of the cellulose chain. The values of the activation energy indicate that the samples change from low semiconductor to high semiconductor property with heating.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1993.052120102
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  • 10
    Electronic Resource
    Electronic Resource
    Conformational studies of stereoisomeric 14-membered cyclic enkephalin analogues containing 1-naphthyialanine at the fourth position: Chirality effect of leucine at the fifth position on biological activity and receptor selectivity (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 877-898 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to study structure-activity relationships of enkephalin-related analogues, we report the biological activity and conformational analysis of four 14-membered cyclic enkephalin analogues with β-(1-naphthyl)alanine in place of phenylalanine at the fourth position, Tyr-c[D-A2bu-Gly-(L and D)-βNal(1)-(L and D)-Leu]. The L-βNal(1)-containing analogues display higher activity at both the μ and δ receptors than the corresponding analogues with the L-Phe residue. In contrast to the linear enkephalins, the cyclic analogues with the D-βNal(1) residue are also active at the μ receptor since the relative spatial arrangement of functional groups required for biological activity is achieved by the constrained nature of the cyclic molecules. A comparison of the findings from the conformational analysis and biological assays establishes that relatively extended structures, in which the two aromatic side chains are oriented in opposite directions with a ∼ 14Å separation, is required for activity at the μ receptor. On the other hand, folded conformations with nearly parallel orientations and a close proximity ( 〈 10Å) of the aromatic rings of the Tyr and βNal(1) residues are required for activity at the δ receptor. It should be noted that the overall structures and thus the biological profiles of the 14-membered cyclic enkephalin analogues are strongly dependent on the conformation of the second residue. The folded conformations with parallel orientation of the two aromatic side chains of Tyr-c [D-A2bu-Gly-L-βNal (1)-D-Leu] is stabilized by an interaction between the Tyr phenolic OH proton and βNal(1) C*O groups. This analogue, which shows the highest activity at both the μ and δ receptors among the four stereoisomers studied, displays an increase of the fraction of the side-chain χ1 = t conformer for the βNal(1) residue. It is concluded that the incorporation of the D-Leu residue at the fifth position increases the relative fraction of the folded conformations with parallel orientation of the aromatic side chains, and hence enhances activity at the δ receptor as compared to the corresponding L-Leu containing analogue.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360310708
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