SUBCELLULAR-DISTRIBUTION AND CHARACTERIZATION OF GLUCOSEPHOSPHATE ISOMERASE IN LEISHMANIA-MEXICANA MEXICANA

The glycolytic enzyme glucosephosphate isomerase (PGI) is present in t wo different cell compartments of Leishmania mexicana promastigotes; m ore than 90% of the activity was detected in the cytosol, the remainde r in glycosomes. This subcellular distribution contrasts with that in Trypanosoma brucei, in which the enzyme activity has been mainly locat ed in the glycosomes. PGI was partially from L. mexicana cell extracts . Throughout the purification procedure only one single PGI activity c ould be detected. The partially purified protein had the same subunit molecular mass (65 kDa) as the previously characterized glycosomal pro tein of T. brucei. Both proteins were also very similar with respect t o their kinetic and antigenic properties. Using the T. brucei glycosom al PGI gene as hybridization probe, we cloned the corresponding gene o f L. mexicana. Only a single PGI locus could be detected in the L. mex icana genome. Characterization of the cloned gene showed that it codes for a polypeptide of 604 amino acids, with a molecular mass of 67113. The sequences of the Leishmania and Trypanosoma polypeptides are 69% identical. They differ in calculated net charge (-8 versus -2, respect ively) and isoelectric point (6.65 versus 7.35). Our data strongly sug gest that the PGI activity in the two cell compartments of L. mexicana and T. brucei is not attributable to different isoenzymes. We discuss the possible metabolic function of the highly different enzyme distri bution in the two organisms, and the molecular mechanism that could be responsible for it.