Substrate specificity and inhibitor sensitivity of a Trypanosoma cruzi alkaline peptidase.

enzyme is a true cathepsin L. No enzyme with properties of cathepsin B were detected in T. cnrzi, although the enzyme described by Cazzulo and co-workers [3-51 has some features in common with cathepsin B. The enzyme that cleaves Ala-Ala-pNA is inhibited by E64, iodoacetic acid and leupeptin, but is not affected by inhibitors of serine, metalloor aspartic peptidases. It does not release p-nitroaniline from Boc-Ala-Ala-pNA or from Ala-Ala-Ala-pNA, and therefore has properties of a cysteine-type dipeptidylaminopeptidase. We are examining the possibility that this enzyme is related to cathepsin C described in other systems. Another enzyme occurs in T. cruzi that cleaves Boc-Ala-Ala-pNA and this enzyme is inhibited by diisopropylfluorophosphate but not by phenylmethanesulphonylfluoride, leupeptin, pepstatin A, ophenanthroline, iodoacetic acid or E64. This serine peptidase is a major activity in epimastigote extracts. However, of all the enzymes that we have detected in T. cmzi epimastigotes, the alkaline peptidase, which characteristically readily cleaves Bz-Arg-pNA, is the most abundant activity. Indeed, this enzyme apparently occurs as a major activity in other trypanosomatids [ 2 ] . Table 1 summarizes the peptidases that we have detected in T. cruzi epimastigotes using chromogenic and fluorogenic substrates.