Transport and Metabolism of Adenosine in Trypanosoma vivax

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Okochi, I.V
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University of Lagos
Transport metabolism of adenosine have been studied in Trypanosoma vivax. In the transport studies, it was found that adenosine uptake was inhibited by different antimetabolites. Phlorizin, coformycin and formycin A produced approximately the same level of inhibition more than ouabain while ouabain inhibited more than iodoacetate. Guanosine stimulated adenosine uptake considerably but neither thymidine nor inosine had any appreciable effect. Results of the time course assay and uptake studies of various concentrations of adenosine suggest that possibly more than one mode of uptake operates in the transport of adenosine in T. vivax. In the metabolic studies, it was observed that adenosine was converted to inosine, hypoxanthine, adenine and nucleotides in whole cells, crude cell extracts and isolated membranes of T. vivax. The major product formed, under the conditions of the present studies, was inosine. Coformycin inhibited the conversion of adenosine to inosine suggesting the presence of adenosine deaminase in this parasite. Formycin A inhibited appreciably the incorporation of 14C-adenosine into nucleic acids in intact cells of T. vivax. It also inhibited the conversion of adenosine to inosine in crude cell extract. The mechanism of action is not definite but probably, formycin A is a substrate to the deaminase in this microorganism. The conversion of inosine to hypoxanthine was stimulated in the presence of exogenous inorganic phosphate. The conversion of hypoxanthine to inosine was increased slightly by the addition of ribose-1-phosphate to the reaction medium, indicating the existence of the action of purine. Nucleoside phosphorylase. In addition, inosine was converted to hypoxanthine in the absence of exogenous inorganic phosphate, suggesting the presence of purine nucleoside hydrolase activity. The data obtained in these studies suggest that adenosine metabolism in T. vivax mimicks that of the mammalian cells. However, differences could exist in the nature of the enzyme systems.
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Transport metabolism of Adenosine , Trypanosoma vivax
Okochi, I.V (1986) Transport and Metabolism of Adenosine in Trypanosomavivax. University of Lagos School of Postgraduate Studies Phd Biochemistry Thesis and Dissertation Abstracts, 157p.