Proteolytic enzymes in human leukemic lymphoid cells. III. Aminopeptidases, angiotensin-converting enzyme, and its inhibitor in cells of different immunological phenotype

Activities of plasma membrane proteinases such as angiotensin-converting en zyme (ACE), aminopeptidases, and dipeptidyl peptidase TV (DPP-IV) were dete rmined in lymphoid cells of various immunological phenotype which were obta ined from 30 patients with lymphoproliferative diseases. The. enzyme activi ties significantly varied depending on the immunological phenotype and stag e of cell differentiation, but no correlation was found between activities of ACE, DPP-IV, and aminopeptidases in the cells of different type. The cel l lysates studied contained at least two classes of aminopeptidases: metal- and sulfhydryl-dependent enzymes. A sulfhydryl-dependent aminopeptidase wi th activity optimum at pH 8.5-9.0 was found for the first time and is sugge sted to be from a poorly studied aminopeptidase family. In addition to ACE, lysates of leukemic T-and B-cells were found to contain an inhibitor of AC E which was not previously described for these cells.