Abstract
MDH1, isoenzyme of malate dehydrogenase from blood stream Trypanosoma vivax was characterized. The enzyme was active over a broad pH and temperature range with optimal values of 5.0 and 35oC respectively. The energy of activation was 20.58kj/mol and the pKa values were 6.8 and 7.8 implicating ionizable groups at the catalytic site. Kinetic studies conducted in the direction of oxaloacetate reduction gave KM of 0.56 and 0.3 mM and Vmax of 4.6 and 3.2 µmol./ min/mg for oxaloacetate and NADH respectively. Similarly, in the reverse reaction, malate had KM of 0.16 Mm and Vmax of 57 µmol./min/mg, and KM and Vmax of NAD+ were 0.1 5 mM and 48 µmol./min/mg. The enzyme was inhibited competitively with NAD+ as a product inhibitor and uncompetitive with malate. The product inhibition studies suggest bi-bi ordered sequential mechanism of catalysis. Some TCA cycle intermediates also inhibited to different extent the activity of the enzyme. Key words: Malate dehydrogenase, Trypanosoma vivax, isoenzyme.
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