Purification and characterization of tripeptidyl peptidase I from Dictyostelium discoideum

10.1080/15216549900202203.absA tripeptidyl peptidase I from Dictyostelium discoideum was purified 744‐fold to near homogeneity. The enzyme is 214 kDa in size and is composed of two monomers with a Mr of 107 kDa. It has two pH optima at pH 4.5 and 5.9 and is a serine peptidase with no aminopeptidase or dipeptidyl peptidase activity. The enzyme was relatively specific showing activity on ala‐ala‐phe‐p‐nitroaniline but also acted on substrates with proline in the Pi position in contrast to mammalian TPP I. The Km values of the enzyme at pH 4.5 for ala‐ala‐phe‐, ala‐phe‐pro‐ and ala‐ala‐pro‐p‐nitroanilines were 271μM, 437μM and 888μM, respectively. The enzyme is most abundant during the amoeba stage of the life cycle but is present in the early stages of development and may therefore have a dual role in the organism in mobilizing amino acids or in processing specific peptides or proteins.