Properties of alpha-hydroxyacid dehydrogenase isozymes from Trypanosoma cruzi

Whole cell extracts of culture epimastigotes of Trypanosoma cruzi (Tulahuén strain) have alpha-hydroxyacid dehydrogenase activity which catalyzes the NAD-linked reaction alpha-ketoacid in equilibrium with alpha-hydroxyacid, with a variety of substrates. Two molecular forms of the enzyme have been separated by means of gel electrophoresis. These isozymes were partially purified by DEAE-cellulose chromatography and ammonium sulfate precipitation. Molecular weights were estimated and some catalytic properties were determined with purified isozymes. The faster migrating fraction (isozyme I) has a molecular weight of 85 500 and showed significant activity against linear 3-5 carbon chain substrates. The lowest Km value was obtained for pyruvate. Isozyme II (MW 60 500) utilizes linear and branched chain substrates with 4-6 carbon atoms. Its highest activity and lowest Km value were recorded with alpha-keto-isocarproate as substrate.