Quantitation of Endopeptidase 24.11 and Endopeptidase 24.15 in Human Blood Leukocytes

Endopeptidase 24.11 (EP 24.11; also called neutral endopeptidase, enkephalinase, CALLA, or CD10) and endopeptidase 24.15 (EP 24.15) are widely distributed neutral metalloendopeptidases that degrade a number of bioactive peptides including substance P, bradykinin, neurotensin, and chemotactic peptides. In this study we used sensitive substrates and specific inhibitors to quantitate the levels of these enzymes in purified peripheral human blood leukocytes obtained from healthy blood donors. We found that neutrophils did not contain detectable amounts of EP 24.15. In contrast, T lymphocytes, B lymphocytes, and monocytes contained significant amounts of the enzyme (446 +/- 248,314 +/- 183, and 484 +/- 212 nmol/mg protein/h, respectively). Neutrophils contained significant amounts of EP 24.11 (266 +/- 130 nmol/mg protein/h). Significantly lower levels of the enzyme were found in T lymphocytes, B lymphocytes, and monocytes (94 +/- 31, 87 +/- 38, and 20 +/- 13 nmol/mg protein/h, respectively). These findings suggest that the effects of some bioactive peptides on peripheral blood leukocyte function may be modulated by these enzymes.