Browsing by Author "Vaidyanathan, C S"
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Item Alterations in the activities of the enzymes of proline metabolism in Ragi (Eleusine coracana) leaves during water stress.(1981-12) Kandpal, Rajendra P; Vaidyanathan, C S; Kumar, M Udaya; Sastry, K S Krishan; Rao, N AppajiFree proline content in Ragi (Eleusine coracana) leaves increased markedly (6 to 85 fold) as the degree of water stress, created by polyethylene gylcol treatment, was prolonged There was also a marginal increase in soluble proteins in the stressed leaves as compared to that in the controls. Water stress stimulated the activities of ornithine aminotransferase and pyrroline-5-carboxylate reductase, the enzymes of proline biosynthesis and markedly inhibited the enzymes involved in proline degradation viz., proline oxidase and pyrroline-5-carboxylate dehydrogenase. These results suggest that increase in free proline content of Ragi leaves could be due to enhanced activities of the enzymes synthesizing proline but more importantly due to severe inhibition of the enzymes degrading proline. These observations establish for the first time, the pathway of proline metabolism in plants by way of detection of the activities of all the enzymes involved and also highlight the role of these enzymes in proline accumulation during water stress.Item Anthranilate hydroxylase, an iron enzyme, from Aspergillus niger.(1979-12-01) Subramanian, V; Sugumaran, M; Vaidyanathan, C SItem Chemical modification of 3-HBA-6-hydroxylase by phenylglyoxal: kinetic and physicochemical studies on the modified enzyme.(1998-10-20) Sumathi, S; Dasgupta, D; Vaidyanathan, C SThe inactivation of 3-HBA-6-hydroxylase isolated from Micrococcus species by phenylglyoxal and protection offered by 3-HBA against inactivation indicate the presence of arginine residue at or near the substrate binding site. The loss of enzyme activity was time and concentration dependent and displayed pseudo-first order kinetics. A 'n' value of 0.9 was obtained thus suggesting the modification of a single arginine residue per active site which led to the loss of enzyme activity. The enzyme activity could be restored by extensive dialysis at neutral pH. Quenching of the intrinsic fluorescence and reduction in the ellipticity value at 280 nm in the near-UV CD spectrum of the enzyme was noticed after its treatment with phenylglyoxal. These observations probably imply distinct perturbations in the environment of adjacent aromatic amino acid residues such as tryptophan as a consequence of arginine modification.Item Effect of phytohormones on nuclear RNA synthesis in germinating seeds of Trigonella foenumgraeceum and its callus.(1979-09) Asha, P K; Shaila, M S; Vaidyanathan, C S; Ramakrishnan, TTreatment of Trigonella foenumgraeceum (fenugreek) seedlings with naphthalene acetic acid plus gibberellic acid enhanced the RNA synthesising capacity of nuclei isolated from the hypocotyl and cotyledonary regions. This increase was more pronounced in the nuclei from the hypocotyl region than from the cotyledonary region. In vitro addition of these phytohormones did not stimulate RNA synthesis by nuclei. The RNA synthesis by mitochondria was not affected by preincubating the seedlings with the hormones. The nuclei isolated from callus cultures of fenugreek hypocotyl treated with the hormone also showed increased RNA synthesis.Item Formation of 2,4-dihydroxybenzoic acid & resorcinol as intermediates in the degradation of salicylic acid by Aspergillus nidulans.(1975-07-01) Ramanarayanan, M; Vaidyanathan, C SItem Immobilization of anthranilate hydroxylase from Aspergillus niger.(1979-06-01) Subramanian, V; Sugumaran, M; Vaidyanathan, C SItem Isolation and cofactor requirements of benzoic acid-4-hydroxylase from Aspergillus niger.(1974-03-01) Reddy, C C; Vaidyanathan, C SItem Kinetic mechanism of gamma glutamyl transferase reaction catalyzed by the mung bean (Phaseolus aureus) glutamine synthetase.(1977-06-01) Seethalakshmi, S; Vaidyanathan, C S; Rao, N AItem m-Hydroxybenzoate 4-hydroxylase from Aspergillus niger: purification and properties.(1973-09-01) Kumar, R P; Rao, P V; Vaidyanathan, C SItem Mandelate oxidase of Aspergillus niger. I. Properties of particulate D(-)-mandelate oxidase.(1973-12-01) Ramanarayanan, M; Vaidyanathan, C SItem Mechanism of aromatic hydroxylation : involvement of perhydroxyl radicals and semiquinones in hydroxylation of aromatic amino acids by a model system.(1975-06-01) Kumar, A A; Rao, B S; Vaidyanathan, C S; Rao, N AItem Mechanism of aromatic hydroxylation : the kinetic mechanism & the involvement of superoxide anions in the reaction catalyzed by m-hydroxybenzoate-4-hydroxylase from Aspergillus niger (UBC-814).(1978-02-01) Kumar, A A; Vaidyanathan, C S; Rao, N AItem Metabolism of benzoate by a soil pseudomonad.(1976-06-01) Reddy, C C; Sugumaran, M; Vaidyanathan, C SItem Oxidation of catechol in plants. II. Enzymic conversion of catechol to diphenylenedioxide 2,3-quinone in the leaves of Tecoma stans L.(1973-03-01) Kandaswami, C; Vaidyanathan, C SItem Purification and properties of D-amino acid oxidas of Aspergillus niger.(1976-09-01) Kishore, G; Vaidyanathan, C SItem RNA polymerase activity in isolated nuclei of Nicotiana sanderae callus: Characteristics and modulation during differentiation.(1983-12) Asha, P K; Shaila, M S; Vaidyanathan, C S; Ramakrishanan, TIsolated nuclei from differentiating cultures of Nicotiana sanderae showed increased levels of RNA polymerase activity as compared to the nuclei from callus cultures. The RNA synthetic activity was dependent on nucleotide triphosphates and Mg2+ and was destroyed by RNase. Maximum activity was obtained in the presence of 50 mM (NH4)2 SO4 and α-amanitin inhibited 40% and 55% of the activity in the nuclei from callus and differentiating tissue respectively. The nuclei from differentiating tissue elicited a 3-fold increase in RNA polymerase I and a 4-fold augmentation in RNA polymerase II activities.Item Role of glutamine synthetase in citric acid fermentation by Aspergillus niger.(1985-06) Punekar, N S; Vaidyanathan, C S; Rao, N AppajiThe activity of glutamine synthetase from Aspergillus niger was significantly lowered under conditions of citric acid fermentation. The intracellular pH of the organism as determined by bromophenol blue dye distribution and fluorescein diacetate uptake methods was relatively constant between 6·0-6·5, when the pH of the external medium was varied between 2·3-7·0. Aspergillus niger glutamine synthetase was rapidly inactivated under acidic pH conditions and Mn2+ ions partially protected the enzyme against this inactivation. Mn2+- dependent glutamine synthetase activity was higher at acidic pH (6·0) compared to Mg2+- supported activity. While the concentration of Mg2+ required to optimally activate glutamine synthetase at pH 6·0 was very high (≥ 50 mM), Mn2+ was effective at 4 mM. Higher concentrations of Mn2+ were inhibitory. The inhibition of both Mn2+ and Mg2+-dependent reactions by citrate, 2-oxoglutarate and ATP were probably due to their ability to chelate divalent ions rather than as regulatory molecules. This suggestion was supported by the observation that a metal ion chelator, EDTA also produced similar effects. Of the endproducts of the pathway, only histidine, carbamyl phosphate, AMP and ADP inhibited Aspergillus niger glutamine synthetase. The inhibitions were more pronounced when Mn2+ was the metal ion activator and greater inhibition was observed at lower pH values. These results permit us to postulate that glutamine synthesis may be markedly inhibited when the fungus is grown under conditions suitable for citric acid production and this block may result in delinking carbon and nitrogen metabolism leading to acidogenesis.Item Role of Mn2+ and Mg2+ in catalysis and regulation of Aspergillus niger glutamine synthetase.(1985-06-01) Punekar, N S; Vaidyanathan, C S; Rao, N AItem A simple and direct method for synthesis of S-mercuric-N-dansylcysteine.(1984-04-01) Kunapuli, S P; Khan, N U; Vaidyanathan, C SItem Studies on Aspergillus niger glutamine synthetase: Regulation of enzyme levels by nitrogen sources and identification of active site residues.(1984-03) Punekar, N S; Vaidyanathan, C S; Rao, N AppajiThe specific activity of glutamine synthetase (L-glutamate: ammonia ligase, EC 6.3.1.2) in surface grown Aspergillus niger was increased 3-5 fold when grown on L-glutamate or potassium nitrate, compared to the activity obtained on ammonium chloride. The levels of glutamine synthetase was regulated by the availability of nitrogen source like NH4 + , and further, the enzyme is repressed by increasing concentrations of NH4 +. In contrast to other micro-organisms, the Aspergillus niger enzyme was neither specifically inactivated by NH4 + or L-glutamine nor regulated by covalent modification. Glutamine synthetase from Aspergillus niger was purified to homogenity. The native enzyme is octameric with a molecular weight of 385,000±25,000. The enzyme also catalyses Mn2+ or Mg2+-dependent synthetase and Mn2+-dependent transferase activity. Aspergillus niger glutamine synthetase was completely inactivated by two mol of phenylglyoxal and one mol of N-ethylmaleimide with second order rate constants of 3·8 M–1 min–1 and 760 M–1 min–1 respectively. Ligands like Mg. ATP, Mg. ADP, Mg. AMP, L-glutamate NH4 +, Mn2+ protected the enzyme against inactivation. The pattern of inactivation and protection afforded by different ligands against N-ethylamaleimide and phenylglyoxal was remarkably similar. These results suggest that metal ATP complex acts as a substrate and interacts with an arginine ressidue at the active site. Further, the metal ion and the free nucleotide probably interact at other sites on the enzyme affecting the catalytic activity.