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Biomedical subjects

K Prabhakaran

Publications and source records attributed to K Prabhakaran.

At least 109 records · Page 6Linked to original sources
PubMed1979

Metabolic inhibitors of host-tissue origin in Mycobacterium leprae.

It is not clear why host-derived bacteria are metabolically inert, compared to organisms grown in vitro. o-Diphenoloxidase is the only metabolic property proven to be present in Mycobacterium leprae separated from infected human as well as animal (mouse and armadillo) tissues. However, highly concentrated suspensions of M. leprae obtained from the organs of experimentally infected armadillos showed little or extremely low o-diphenoloxidase, while the organisms bound 14C-labeled dopa. When these preparations were diluted, they readily oxidized D-dopa to pigment. The activity remained unaltered by washing the suspensions with dilute alkali or acetone and ether, indicating that it is an intrinsic property of the bacilli. Treatment with different proteases relieved the inhibition, and resulted in a 100% stimulation of O-diphenoloxidase in the bacilli. Evidently, the M. leprae suspensions obtained from infected tissues contain an inhibitory material which is protein in nature, and the metabolic inertness sometimes observed in host-grown bacteria may not be due to loss of enzymes or metabolites from the organisms.

Animals↗
PubMed1976

5-thio-D-glucose: o-diphenoloxidase inhibition as its mechanism of action.

5-Thio-D-glucose completely inhibited o-diphenoloxidase from animal as well as plant sources. It has been reported that thioglucose suppresses spermatogenesis in mice and also insect metamorphosis, probably through inhibition of glucose transport. Inhibition of o-diphenoloxidase (which is active in spermatozoa and insect larvae) is suggested as an alternative mechanism of action of thioglucose.

Basidiomycota↗
PubMed1976

Hyaluronic acid and yeast extract do not oxidize DOPA.

Hyaluronic acid and yeast extract, separately and in combination, were tested for their ability to oxidize dopa to pigment. Two types of hyaluronic acid and yeast extract were used. The activities were assayed both spectrophotometrically and by oxygen-uptake determinations. The results were uniformly negative. The biological role of hyaluronic acid is discussed. Use of pigment formation from phenolic compounds as an identification test of another organism is pointed out.

Catechol Oxidase↗
PubMed1975

o-Diphenoloxidase of Mycobacterium leprae separated from infecected armadillo tissues.

We reported earlier the occurrence of a unique o-diphenoloxidase in Mycobacterium leprae recovered from lepromatous human tissues. No other source of M. leprae fro biochemical studies was available at the time. In the present report, properties of phenoloxidase in M. leprae separated from infected armadillo tissues are presented. The results show that the o-diphenoloxidase remains unaltered in the passage of the bacilli from the human to the the animal host, indicating that the enzyme is an intrinsic characteristic of the leprosy bacteria.

Animals↗
PubMed1975

Uptake of radioactive DOPA by Mycobacterium leprae in vitro.

Our previous studies demonstrated that Mycobacterium leprae contains a characteristic o-diphenoloxidase which converts a variety of phenolic compounds to quinones in vitro. This enzyme was not present in any other mycobacteria tested. The results reported here deal with the uptake and binding of radioactive DOPA by M. leprae. The leprosy bacilli incubated with tritium-labelled DOPA, readily took up the substrate. The binding of DOPA by the bacilli was markedly inhibited by diethyldithiocarbamate. The organisms also bound tritiated norepinephrine. Mycobacterium phlei which does not oxidize phenolic substrates failed to bind DOPA. Cultures of melanocytes which contain o-diphenoloxidase took up tritiated DOPA. Catecholamine metabolism is known to be important in myocardial cells. Cultures of turtle-heart cells did not oxidize DOPA to quinone; however, these cells bound the labelled substrate. A cell line of fibroblasts derived from armadillo skin neither oxidized nor took up DOPA. The results indicate that, like melanocytes and turtle-heart cells, M. leprae probably possesses specific receptor sites for the binding and subsequent metabolism of phenolic substrates.

Animals↗
PubMed1971

Unusual effects of reducing agents on 0-diphenoloxidase of Mycobacterium leprae.

Reducing agents had no effect on the oxidation of 3,4-dihydroxyphenylalanine (DOPA) to quinone by Mycobacterium leprae; no quinone formation by o-diphenoloxidase of mammalian or plant origin was detected under similar experimental conditions. Ascorbic acid and reduced glutathione prevented further oxidation and polymerization of the quinone to melanin by M. leprae; cysteine was less effective. In the presence of reducing agents, the quinone (indole-5,6-quinone) formed from DOPA by M. leprae was not reduced back to diphenol. On the other hand, the quinone (dopachrome) produced from DOPA by mammalian or plant phenolase was rapidly decolorized by reducing agents. Oxidized glutathione and cystine had little effect on o-diphenoloxidase from all of the three sources. Cyanide, which completely inhibited mammalian and plant phenolases, had only a partial effect on the enzyme in the bacilli. Various lines of evidence suggest that the properties of o-diphenoloxidase in M. leprae are different from those of similar enzymes obtained from other sources.

Animals↗