[Alpha-hydroxy-acid dehydrogenase activity in Trypanosoma cruzi].

Crude extracts of culture forms of epimastigotes, Tulahuén strain, showed activity to catalyze the reaction alpha-ketocid in equilibrium alpha-hydroxyacid linked to nicotinamide adenine dinucleotide (NAD). The enzyme utilizes the following substrates: alpha-ketobutyrate, alpha-ketoisovalerate, alpha-keto-beta-methylvalerate, alpha-ketocaproate, alpha-ketoisocaproate, alpha-ketoglutarate and pyruvate. Kinetics for the three last substrates were of the Michaelian type. For the other ketocids, curves of activity against substrate concentration exhibited a bimodal character. Km and V values for alpha-ketoisocaproate were strikingly higher than those for the other substrates. Electrophoretic separation of extracts on polyacrylamide gel and specific staining showed a single zone of enzymatic activity with similar mobility for all the alpha-OH-acids tested. This finding would indicate that the same protein is responsible for the reaction. The observations presented demonstrate that culture forms of Trypanosoma cruzi possess the ability to interconvert pyruvate in equilibrium lactate and to regenerate NAD in anaerobiosis. Although the physiological significance of the reaction with alpha-ketoacids other than pyruvate is not known, similarity of substrate of substrate spectrum between alpha-OH-acid dehydrogenase from Trypanosoma cruzi and lactate dehydrogenase ioenzyme X from mammalian and avian spermatozoa is interesting. Perhaps activity of flagella requires analogous metabolic pathways.