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Biomedical subjects

C S Vaidyanathan

Publications and source records attributed to C S Vaidyanathan.

At least 37 records · Page 2Linked to original sources
PubMed1989

Enzyme catalysed non-oxidative decarboxylation of aromatic acids. II. Identification of active site residues of 2,3-dihydroxybenzoic acid decarboxylase from Aspergillus niger.

In order to understand the mechanism of decarboxylation by 2,3-dihydroxybenzoic acid decarboxylase, chemical modification studies were carried out. Specific modification of the amino acid residues with diethylpyrocarbonate, N-bromosuccinimide and N-ethylmaleiimide revealed that at least one residue each of histidine, tryptophan and cysteine were essential for the activity. Various substrate analogs which were potential inhibitors significantly protected the enzyme against inactivation. The modification of residues at low concentration of the reagents and the protection experiments suggested that these amino acid residues might be present at the active site. Studies also suggested that the carboxyl and ortho-hydroxyl groups of the substrate are essential for interaction with the enzyme.

Aspergillus niger↗
PubMed1988

Purification and properties of 4-hydroxyphenylacetic acid 3-hydroxylase from Pseudomonas putida.

4-Hydroxyphenylacetic acid 3-hydroxylase is a key enzyme in the pathway for the microbial degradation of phenylalanine, tyrosine and many aromatic amines. This enzyme was purified to homogeneity from Pseudomonas putida by affinity chromatography. The protein had a molecular weight of 91,000 and was a dimer of identical subunits. It was a typical external flavoprotein monooxygenase and showed an absolute requirement of NADH for activity. The enzyme had a pH optimum of 7.5 and the Km values for 4-hydroxyphenylacetic acid and NADH were 2 x 10(-4) M and 5.9 x 10(-5) M respectively. It was strongly inhibited by heavy metal ions and thiol reagents, suggesting the possible involvement of -SH group(s) in enzyme reaction.

Hydrogen-Ion Concentration↗
PubMed1987

Enzyme-catalysed non-oxidative decarboxylation of aromatic acids: I. Purification and spectroscopic properties of 2,3 dihydroxybenzoic acid decarboxylase from Aspergillus niger.

In order to understand the molecular mechanism of non-oxidative decarboxylation of aromatic acids observed in microbial systems, 2,3 dihydroxybenzoic acid (DHBA) decarboxylase from Aspergillus niger was purified to homogeneity by affinity chromatography. The enzyme (Mr 120 kDa) had four identical subunits (28 kDa each) and was specific for DHBA. It had a pH optimum of 5.2 and Km was 0.34 mM. The decarboxylation did not require any cofactors, nor did the enzyme had any pyruvoyl group at the active site. The carboxyl group and hydroxyl group in the ortho-position were required for activity. The preliminary spectroscopic properties of the enzyme are also reported.

Aspergillus niger↗
PubMed1985

In vivo and in vitro destruction of rat liver cytochrome P-450 by a monoterpene ketone, pulegone.

In vivo administration of pulegone once daily decreased the levels of liver microsomal cyt. P-450 to the extent of 32 and 76% at the end of 24 and 96 hrs respectively. However, cyt. b5 and NAD(P)H-cyt. c reductase activities remained unchanged. In vitro incubation (15 min) of liver microsomes from phenobarbitol (PB)-treated rats with pulegone (10 mM), aerobically or anaerobically resulted in the loss (approximately 60%) of cyt. P-450 in the presence or absence of NADPH. Destruction of cyt. P-450 was more in PB-treated microsomes as compared to 3-methylcholanthrene (MC)-treated and control microsomes. The loss of cyt. P-450 was accompanied by a concomitant loss of microsomal heme. In contrast, menthone or carvone upon incubation with PB-induced microsomes resulted in the conversion (25-40%) of cyt. P-450 to cyt. P-420 without any loss of microsomal heme. The destructive process is irreversible, time dependent, linear upto a substrate concentration of 10 mM and follows first order kinetics.

Administration, Oral↗
PubMed1985

An essential arginine residue at the substrate binding site of 4-hydroxyisophthalate hydroxylase.

4-Hydroxyisophthalate hydroxylase was inactivated by treatment with phenylglyoxal by a process obeying pseudo-first order kinetics indicating the presence of an essential arginine located presumably in the active site. Addition of saturating amounts of 4-hydroxyisophthalate during the treatment resulted in complete protection of the enzyme from the inactivation, but addition of NADPH was totally ineffective. Analysis of the effect of various substrate analogs on the protection of the enzyme showed that carboxyl and hydroxyl groups at para positions on the aromatic ring are essential for substrate binding to the active site. It was also observed that analogs which protect the enzyme against phenylglyoxal inactivation are themselves effective inhibitors of the enzyme activity.

Arginine↗
PubMed1984

Anthranilate hydroxylase from Aspergillus niger: new type of NADPH-linked nonheme iron monooxygenase.

Anthranilate hydroxylase from Aspergillus niger catalyzes the oxidative deamination and dihydroxylation of anthranilic acid to 2,3-dihydroxybenzoic acid. This enzyme has been purified to homogeneity and has a molecular weight of 89,000. The enzyme is composed of two subunits of 42,000 with 2 gram-atoms of nonheme iron per mol. Fe2+-chelators like alpha,alpha'-dipyridyl and o-phenanthroline are potent inhibitors of the enzyme activity. Absorption and fluorescence spectra of the enzyme offer no evidence for the presence of other cofactors like flavin. Flavins and flavin-specific inhibitors like atebrin have no effect on the activity of the enzyme. The enzyme incorporates one atom of oxygen each from 18O2 and H218O into the product 2,3-dihydroxybenzoic acid. Based on these studies, it is concluded that anthranilate hydroxylase from A. niger is a new type of NADPH-linked nonheme iron monooxygenase.

Aspergillus niger↗
PubMed1984

A new 4-nitrophenol 2-hydroxylase from a Nocardia sp.

A new enzyme which can hydroxylate 4-nitrophenol to 4-nitrocatechol has been isolated from a Nocardia sp. It is an inducible enzyme found in the 105,000xg supernatant. It requires molecular oxygen, reduced pyridine nucleotide, and flavin adenine dinucleotide for its activity. Preliminary characterization of this enzyme is reported in this communication.

Catechols↗
PubMed1983

Purification and Characterization of a New Indole Oxygenase from the Leaves of Tecoma stans L.

A new indole oxygenase from the leaves of Tecoma stans was isolated and purified to homogenity. The purified enzyme system catalyzes the conversion of indole to anthranilic acid. It is optimally active at pH 5.2 and 30 degrees C. Two moles of oxygen are consumed and one mole of anthranilic acid is formed for every mole of indole oxidized. Dialysis resulted in complete loss of the activity. The inactive enzyme could be reactivated by the addition of concentrated dialysate. The enzyme is not inhibited by copper-specific chelators, non-heme iron chelators or atebrin. It is not a cuproflavoprotein, unlike the other indole oxygenases and oxidases.

Journal Article↗
PubMed1977

Metabolism of monoterpene alcohol, linalool, by a soil pseudomonad.

A microorganism of the genus Pseudomonas has been isolated from the soil by enrichment culture techniques with linalool(I) as the sole source of carbon and energy. The organism is also capable of utilizing limonene, citronellol, and geraniol as substrates but fails to grow on citral, critranellal, and 1,8-cineole. Fermentation of linalool by this bacterium in a mineral salt medium results in the formation of 10-hydroxylinalool(II), oleuropeic acid (IX), 2-vinyl-2-methyl-5-hydroxyisopropyl-tetraphydrofuran)linalool oxide, V), 2-vinyl-2-methyl-tetrahydrofuran-5-one(unsaturated lactone, VI), and few unidentified minor metabolities. Probable pathways for the biodegradation of linalool are presented.

Biodegradation, Environmental↗