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Biomedical subjects

K Venkatesan

Publications and source records attributed to K Venkatesan.

49 records · Page 3Linked to original sources
PubMed1977

Structural and kinetic studies on the activators of succinate dehydrogenase.

1. Diverse classes of compounds such as dicarboxylates, pyrophosphates, quinols and nitrophenols are known to activate mitochondrial succinate dehydrogenase (EC 1.3.99.1). Examples in each class -- malonate, pyrophosphate, ubiquinol and 2,4-dinitrophenol -- are selected for comparative studies on the kinetic constants and structural relationship. 2. The activated forms of the enzyme obtained on preincubating mitochondria with the effectors exhibited Michaelian kinetics and gave double-reciprocal plots which are nearly parallel to that of the basal form. On activation, Km for the substrate also increased along with V. The effectors activated the enzyme at low concentrations and inhibited, in a competitive fashion, at high concentrations. The binding constant for activation was lower than that for inhibition for each effector. 3. These compounds possess ionizable twin oxygens separated by a distance of 5.5 +/- 0.8 A and having fractional charges in the range of -0.26 to -0.74 e. The common twin-oxygen feature of the substrate and the effectors suggested the presence of corresponding counter charges in the binding domain. The competitive nature of effectors with the substrate for inhibition further indicated the close structural resemblance of the activation and catalytic sites.

Dinitrophenols↗
PubMed1977

Conformational studies on cyclic dipeptides.

An analysis of 11 crystal structures of cyclic dipeptides so far reported in the literature is made, with main reference to the internal parameters of these molecules. Preferred conformations of the side chains of cyclic dipeptides with different alpha-amino acid residues have been studied by classical energy calculations. The possible conformations of the DKP ring are also studied. The significance of the non-bonded interaction in deciding the pathway for conformational change has also been investigated. The agreement between theoretical results and experimental observations is quite good, both with respect to the conformation of these molecules as well as the enthalpy difference as estimated from n.m.r. studies between different conformers.

Amino Acid Sequence↗
PubMedDate not supplied

Correlation between inhibitory effect of quinolones and mycolic acid metabolism in mycobacteria.

Mycolic acids are important components having a significant role in maintaining the rigidity of mycobacterial cell wall. They could also be the barrier for penetration of certain drugs into the bacterial cell. A novel in vitro model system was established for assessing the effect of Ciproflaxacin on mycolic acid metabolism in pathogenic mycobacteria M. Kansasii (which has similar mycolic acid pattern to that from M. leprae) and the effect of norfloxacin in M. intracellulare. These test mycobacteria were exposed in their midlogarithmic phase of growth to 0.5, 1, 2, 3, 4, 5 and 6 micrograms ml of ciprofloxacin and norfloxacin respectively for 1, 2 and 24 hours. Ciprofloxacin completely inhibited the synthesis of mycolates in M. kansasii at 3, 4 and 5 micrograms/ml; whereas norfloxacin exhibited its maximum inhibitory action on mycolic acids in M. intracellulare at 6 micrograms/ml for all the durations of exposure. Inhibition of mycolates directly correlated with bacterial viability which was estimated by colony forming units. The effect of quinolones on mycolic acid metabolism appears to be direct and not secondary to DNA gyrase. The results obtained from this study and our previous findings show that mycolic acid metabolism is affected by various groups of drugs, whose primary sites of activity may be different. The findings of the present study may have significant therapeutic implications in leprosy and other mycobacterial diseases.

Ciprofloxacin↗
PubMedDate not supplied

Evaluation of effectiveness of clofazimine therapy. I. Monitoring of absorption of clofazimine from gastrointestinal tract.

The quantity of clofazimine absorbed from the gastrointestinal tract when administered to lepromatous leprosy patients at varying single doses of 600 mg., 400 mg., 300 mg., and 100 mg. has been worked out by determining the amount of clofazimine present in total faecal excreta. Except in 100 mg. dose where the percentage absorption was 62.5 +/- 17 in all other case the values were around 45%. The efficacy of daily administration of 100 mg. clofazimine is discussed in this first article.

Clofazimine↗
PubMedDate not supplied

Alanine dehydrogenase in mycobacteria--a preliminary report.

Various mycobacterial species namely M. phlei, M. vaccae, M. scrofulaceum, M. avium and M. tuberculosis have been investigated for the presence of enzyme alanine dehydrogenase which could be important for utilization of alanine by TCA cycle. It was found that alanine dehydrogenase was present in all species of mycobacteria tested irrespective of the fact whether they are rapid or slow growers. Electrophoretic mobilities of alanine dehydrogenase from different species of mycobacteria were not found to be significant for taxonomical differentiation of rapid and slow growers.

Alanine Dehydrogenase↗
PubMedDate not supplied

Bioavailability of dapsone on oral administration of Dapsomine--a comparative evaluation.

This study describes a comparative evaluation of dapsone kinetics in humans on administration of Dapsomine, a capsule containing dapsone 100 mg dispersed in oily-base suspension of clofazimine 50 mg. Seven untreated lepromatous leprosy patients were given one capsule of Dapsomine a day for seven days and the pharmacokinetics parameters in this group were compared with those from another group of seven patients who received dapsone 100 mg and clofazimine 50 mg separately. There were no statistically significant differences in parameters such as peak dapsone plasma concentration (Cmax), basal plasma level (C24h), time to peak level (tmax), absorption half-life (t1/2 alpha), elimination half-life t1/2 beta) and areas under plasma concentration-time curves (AUC0-8h) and AUC0-24h) between the two groups.

Biological Availability↗