Subcellular localization of a cysteine proteinase from Trypanosoma cruzi.

Epimastigotes of Trypanosoma cruzi, Tulahuén strain, Tul 2 stock, contain a cysteine proteinase able to degrade azocasein at pH 5. This enzyme activity was extracted from whole cells by digitonin concentrations higher than those required for cytosolic markers, lower than those required for glycosomal and mitochondrial markers, and very similar to those required for solubilization of the acidic alpha-mannosidase. Both, the azocasein-degrading proteinase and the alpha-mannosidase, showed similar latency and distribution in subcellular fractions (the large granule fraction was the most active), and the same behavior in isopycnic sucrose gradient centrifugation; a broad peak centered at an equilibrium density of about 1.15 g cm-3, with a shoulder between 1.07 and 1.10 g cm-3, was obtained for both enzymes. The results suggest that the cysteine proteinase activity is placed in the lysosomes.