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Biomedical subjects

T A Venkitasubramanian

Publications and source records attributed to T A Venkitasubramanian.

At least 19 recordsLinked to original sources
PubMed1993

Serodiagnostic efficiency of phospholipid associated protein of Mycobacterium tuberculosis H37Rv.

The phospholipid-associated protein (55-67 kDa) fraction of Mycobacterium tuberculosis H37Rv was purified as the DE-V protein fraction. This DE-V fraction was used for diagnosis of tuberculosis by enzyme-linked immunosorbent assay (ELISA), detecting IgG antibody in sera collected from different categories of tuberculosis patients, i.e. with acid fast bacilli (AFB) culture-positive pulmonary tuberculosis, with AFB culture-negative, but radiologically suspected, pulmonary tuberculosis, extrapulmonary tuberculosis, and control groups of patients suffering from diseases other than tuberculosis (asthma and/or rhinitis, lepromatous leprosy) as well as from healthy volunteers. Encouraging operational ELISA validity could be achieved with 93% sensitivity, 100% specificity, 97% efficiency, 100% positive predictivity and 95% negative predictability even among the extrapulmonary and suspected pulmonary tuberculosis patients. The above assay was insensitive but with 100% specificity among control group of patients suffering from diseases other than tuberculosis. The DE-V protein fraction was associated with phosphatidyl inositol and phosphatidyl inositol mannosides. The dissociation of phospholipid-protein complex decreased ELISA specificity. ELISA reactivity of the DE-V fraction appeared to be thermostable; thus, it may have serodiagnostic utility in developing countries.

Antibodies, Bacterial↗
PubMed1991

Calmodulin-like protein and the phospholipids of Mycobacterium smegmatis.

When Mycobacterium smegmatis TMC1546 was grown at different concentrations of glucose supplemented to a synthetic medium already containing 2% v/v glycerol, the following changes were observed. Amount of calmodulin-like protein (CAMLP), total and individual phospholipids (PLs) namely phosphatidylethanolamine, cardiolipin, phosphatidylglycerol and phosphatidylinositol mannosides and total lipids and growth increased up to 5% w/v but decreased at higher concentrations of glucose (7.5% w/v and above). Cyclic AMP content of the whole cells decreased continuously with increase in glucose concentration in the medium. Incorporation of 32Pi into total phospholipids was inhibited by two calmodulin antagonists trifluoperazine and phenothiazine (50% at 40 microM) and the calcium-specific chelator ethylene glycol bis (beta-aminoethyl ether) N,N,N',N'-tetraacetate (EGTA) 35% at 2 mM. Total lipids, CAMLP and growth of this organism are also modulated in a similar way in response to the glucose concentration in the growth medium. Taking these observations together it is suggested that CAMLP has some effect on the metabolism of PLs.

Calcium↗
PubMed1988

Purification and properties of aspartate transcarbamylase from Mycobacterium smegmatis.

Aspartate transcarbamylase (carbamoyl-phosphate: L-aspartate carbamoyltransferase, EC 2.1.3.2) has been purified from Mycobacterium smegmatis TMC 1546 using streptomycin sulphate precipitation, ammonium sulphate precipitation, DE-52 chromatography, second ammonium sulphate precipitation, Sephadex G-200 gel filtration, and aspartate-linked CNBr-activated Sepharose 4B affinity chromatography in successive order. The enzyme was purified 231.6-fold, and the preparation was found to be homogeneous on column chromatography and polyacrylamide gel electrophoresis. The purified enzyme had a molecular weight of 246,000 and was composed of two asymmetrical subunits. The kinetic and regulatory properties of aspartate transcarbamylase from M. smegmatis were also studied. The enzyme was found to be an allosteric in nature with carbamyl phosphate showing positive cooperativity and UMP exhibiting a negative cooperativity. CTP was found to be the most potent inhibitor among nucleotides. Phosphate acted as a non-competitive product inhibitor with respect to aspartate. Succinate and maleate exerted a competitive inhibition when aspartate was the variable substrate.

Allosteric Regulation↗
PubMed1988

A Ca2+-sensitive cyclic-3',5'-nucleotide phosphodiesterase from sheep lung modulated by a tightly bound endogenous calmodulin.

Highly purified sheep lung cyclic-3',5'-nucleotide phosphodiesterase was sensitive to Ca2+/EGTA but insensitive to exogenous calmodulin. The Ca2+-sensitivity was inhibited by trifluoperazine. Heat-treated enzyme could activate a calmodulin-deficient phosphodiesterase, suggesting the presence of endogenous calmodulin in sheep lung cyclic-3',5'-nucleotide phosphodiesterase, possibly associated with the enzyme in a Ca2+-independent manner.

Animals↗
PubMed1988

Temperature and thiol-induced desensitization of a Ca2+-sensitive cyclic-3',5'-nucleotide phosphodiesterase from sheep lung.

Ca2+-sensitivity of sheep lung cyclic-3',5'-nucleotide phosphodiesterase is provided by endogenous tightly bound calmodulin. The calcium sensitivity of a highly purified enzyme was desensitized by increasing the assay temperature. It could also be desensitized to Ca2+-activation by thiols such as dithiothreitol. The thiol-induced desensitization could be partially reversed by dialysis and almost completely reversed by dilution. The results presented in this paper indicate that thiols are possibly involved in the interaction of calmodulin with cyclic-3',5'-nucleotide phosphodiesterase. This is the first report on temperature and thiol-induced desensitization of Ca2+-sensitivity of a cyclic-3',5'-nucleotide phosphodiesterase.

Animals↗
PubMed1987

NADP-specific isocitrate dehydrogenase of Mycobacterium phlei ATCC 354: purification and characterization.

NADP-dependent isocitrate dehydrogenase (EC 1.1.1.42) from Mycobacterium phlei ATCC 354 was purified to homogeneity by ammonium sulphate fractionation, followed by DEAE cellulose and Sephadex G-200 chromatography. The pH optimum of the enzyme was 8.5. The Km values for isocitrate and NADP were 74 and 53 microM, respectively. Mn2+ was essential for enzyme activity. The enzyme lost all activity on incubation at 70 degrees C for 15 min; isocitrate and NADP protected against this thermal inactivation. p-Chloromercuribenzoate inhibited the enzyme; pre-incubation of enzyme with isocitrate + Mn2+ prevented this inhibition. The purified enzyme showed concerted inhibition by glyoxylate + oxaloacetate and was inhibited by oxalomalate.

Glyoxylates↗
PubMed1986

Changes in liver polyamines due to aflatoxin B1.

Changes in liver polyamines of rats and mice of both sexes injected with aflatoxin B1 (AFB1) were determined. AFB1 significantly enhanced liver polyamines of both susceptible and resistant animals, viz. rats and mice, respectively. Sex appears to have little influence on AFB1-mediated stimulation of liver polyamine levels. AFB1 significantly reduced liver polyamine in growing rats reflecting the inhibitory effect of this carcinogen on induced polyamine synthesis.

Aflatoxin B1↗
PubMed1986

Regulation of aflatoxin biosynthesis: effect of adenine nucleotides, cyclic AMP and N6-O2' -dibutyryl cyclic AMP on the incorporation of (1-14C)-acetate into aflatoxins by Aspergillus parasiticus NRRL-3240.

Adenosine triphosphate (ATP) was found to inhibit the incorporation of labelled acetate into aflatoxins while adenosine diphosphate (ADP) and adenosine monophosphate (AMP) stimulated the process. Exogenous cyclic AMP and its derivative, N6-O2' -dibutyryl cyclic AMP produced efficient (1-14C)-acetate incorporation into aflatoxins at all the concentrations tried (0.1, 0.5 and 1 mM). The stimulation of incorporation of labelled acetate into aflatoxins was significant at 0.1 and 1 mM concentration of the cyclic nucleotide but was found to be maximum at 0.5 mM concentration.

Acetates↗
PubMed1986

Nitrogen metabolism in Aspergillus parasiticus NRRL 3240 and A. flavus NRRL 3537 in relation to aflatoxin production.

The relationship between nitrogen assimilation, metabolism and aflatoxin formation has been investigated in a toxigenic and a non-toxigenic strain of Aspergillus parasiticus. Ammonia from the medium is mainly assimilated via NADP-requiring glutamate dehydrogenase. During growth NAD-requiring glutamate dehydrogenase followed an inverse pattern of activity with respect to NADP glutamate dehydrogenase. Alpha-ketoglutarate, the product of NAD glutamate dehydrogenase, stimulated acetate incorporation into aflatoxins. Glutamine synthetase, ornithine transcarbamylase, both utilizing glutamate as substrate were assayed under different growth conditions. An important regulatory role for glutamine synthetase is suggested. The metabolic route of asparagine utilization was also investigated. Both the known pathways, glutamate oxaloacetate transaminase and glutamate pyruvate transaminase are operative simultaneously.

Aflatoxins↗
PubMed1986

3-MHPG as a non-predictor of antidepressant response to imipramine and electroconvulsive therapy.

The urinary excretion of 3-methoxy, 4-hydroxyphenyl-glycol, (3-MHPG) was measured in 20 unipolar depressed patients before treatment with imipramine and electroconvulsive therapy (ECT) to investigate the relationship between pretreatment urinary excretion of 3-MHPG and clinical response. There was no difference in 3-MHPG excretion for depressed patients and controls. There was no significant difference between the mean percentage reduction of Hamilton Depression Rating Scale Scores in "low" and "high" excretors of 3-MHPG in the imipramine and ECT group of patients after four weeks of treatment.

Adult↗
PubMed1986

Ornithine transcarbamylase from Mycobacterium smegmatis ATCC 14468: purification, properties, and reaction mechanism.

Ornithine transcarbamylase (EC 2.1.3.3) has been purified 980-fold from Mycobacterium smegmatis and has a molecular weight of 116,000. Initial velocity determinations indicated that the reaction proceeds via a sequential kinetic mechanism. The limiting Michaelis constants for carbamyl phosphate (KmA) and ornithine (KmB) and the dissociation constant for carbamyl phosphate (Kia) were found to be 0.20, 0.25, and 0.07 mM, respectively. Ornithine at higher concentrations acted as an uncompetitive inhibitor when carbamyl phosphate was the variable substrate. Phosphate was a competitive inhibitor with carbamyl phosphate as variable substrate and showed noncompetitive or mixed type inhibition when ornithine was the variable substrate. Norvaline acted as a competitive inhibitor with ornithine as variable substrate and as an uncompetitive inhibitor when carbamyl phosphate was the variable substrate. Such inhibitory patterns are characteristic of reactions that proceed via sequential ordered mechanisms. Although the enzyme activity was strongly inhibited by arginine, several arginine analogs had no effect on the enzyme activity. The results suggest that, even though the enzyme from M. smegmatis is unique in the sense that it is feedback inhibited by arginine, the reaction mechanism is similar to the ornithine transcarbamylase isolated from other microorganisms.

Amines↗
PubMed1986

Metabolic potential of the adipose tissue of rats during hyper- and hypovitaminosis A.

Effect of excess feeding and depletion of vitamin A on the ability of adipose tissue to maintain plasma free fatty acid levels has been studied in rats. Both in hypervitaminosis A (fed 9 mg of retinol for 2 consecutive days) and in vitamin A deficiency (kept on a vitamin A-deficient diet for 6 weeks) the rats showed elevated levels of plasma free fatty acids. Hypervitaminosis A caused a decrease in the fatty acid release from adipose tissue on in vitro incubation, probably due to lowered levels of cyclic AMP. On the other hand, adipose tissue from vitamin A-deficient animals showed an increased lipolytic rate as compared to that of the controls. No change in the lipogenic ability was indicated in either of the conditions as indicated by the activities of enzymes involved in this process. We conclude that the fatty acid homeostasis can be greatly influenced by the vitamin A status of the animals.

ATP Citrate (pro-S)-Lyase↗
PubMed1984

Characterization and metabolism of cyclic guanosine 3'5'-monophosphate in Mycobacterium smegmatis.

Cyclic guanosine 3'5'-monophosphate was isolated and purified from Mycobacterium smegmatis TMC 1515 using ion exchange chromatography. It was characterized by thin layer chromatography and radioimmunoassay. Guanylate cyclase and cGMP phosphodiesterase were detected in the cytosolic and particulate (37,000 X g pellet) fractions respectively. On the basis of our observations, cGMP appears to play a dual role (i) at the time of induction of cell proliferation and (ii) protects the bacteria against unfavourable surroundings during stationary phase of the growth. This is the first report demonstrating presence of cGMP, guanylate cyclase and cGMP phosphodiesterase in mycobacteria.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1984

Effect of aluminium and nickel on aflatoxin production by Aspergillus flavus.

Effect of nickel and aluminium was studied on aflatoxin and lipid production by two strains of Aspergillus flavus in a sucrose-asparagine-salts medium. Inclusion of aluminium in the medium established an inverse relationship between aflatoxin and lipid production. At lower concentrations aluminium stimulated aflatoxin production, whereas at higher concentrations it stimulated total lipid production. Nickel at higher concentrations resulted in an increase in total aflatoxin production. However, no definite correlation was observed between total aflatoxin and total lipid production when nickel was included in the medium.

Aflatoxins↗
PubMed1983

Purification and properties of pyruvate kinase from Mycobacterium smegmatis.

Pyruvate kinase (ATP:pyruvate 2-O-phosphotransferase, EC 2.7.1.40) from Mycobacterium smegmatis has been purified to homogeneity through a seven-step procedure with a yield of 16% and specific activity of 220 units/mg protein. The purified enzyme had a molecular weight of 230,700 and was composed of four subunits with identical molecular weights of 57,540. Analysis of amino acid composition revealed a low content of aromatic amino acids. The enzyme exhibited sigmoidal kinetics of varying concentrations of phosphoenolpyruvate, the degree of cooperativity and S0.5v value for phosphoenolpyruvate being strongly dependent on the pH of the reaction mixture. Among the nucleoside diphosphates acting as substrate for pyruvate kinase, ADP was the best phosphate acceptor, as judged by its lowest Km value. The enzyme showed an absolute requirement for divalent cations (either Mg2+ or Mn2+), but monovalent cations were not necessary for activity. Other divalent cations inhibited the Mg2+-activated enzyme to varying degrees (Ni2+ greater than Zn2+ greater than Cu2+ greater than Ca2+ greater than Ba2+). The differences in the kinetic responses of the enzyme to Mg2+ and Mn2+ are discussed.

Adenosine Triphosphate↗