Identification of two zinc metalloendopeptidases in alveolar macrophages of rats, guinea pigs, and human beings
Lesser, M.; Fung, K.; Choi, H.S.; Yoo, O.H.; Cardozo, C.
Journal of Laboratory and Clinical Medicine 120(4): 597-603
1992
ISSN/ISBN: 0022-2143 PMID: 1402335 Document Number: 395777
Neutral endopeptidases EC 3.4.24.11 and EC 3.4.24.15, widely distributed zinc metalloendopeptidases, degrade a number of biologically active peptides including substance P, bradykinin, neurotensin, and luteinizing hormone-releasing hormone. In this study we measured EC 3.4.24.11 and EC 3.4.24.15 activity in alveolar macrophages, key inflammatory cells in the lung that produce and respond to a large number of bioactive substances including chemotactic peptides, with the substrates glutaryl-ala-ala-phe-2-naphthylamide and tertiary butoxycarbonyl-phe-ala-ala-phe-paraaminobenzoate, respectively. We found that specific activity of EC 3.4.24.15, defined as activity inhibited with N-((1RS)-carboxy-3-phenylpropyl)-ala-ala-phe-paraaminobenzoate, was significantly higher (p lt 0.001) in cells from Sprague-Dawley rats (485 +- 123 nmol/mg protein cntdot hr) than in cells from Hartley guinea pigs (138 +- 94 nmol/mg protein cntdot hr), healthy human male smokers (121 +- 73 nmol/mg protein cntdot hr) and healthy human male nonsmokers (94 +- 12). In contrast, activity of EC 3.4.24.11, defined as activity inhibited with N-((1RS)-carboxy-3-phenylpropyl)-phe-paraaminobenzoate, was significantly higher (p lt 0.001) in cells from human smokers (698 +- 167 nmol/mg protein cntdot hr) and nonsmokers (762 +- 136 nmol/mg protein cntdot hr) than in cells from rats (52 +- 12 nmol/mg protein cntdot hr) and guinea pigs (34 +- 14 nmol/mg protein cntdot hr). An additional activity in alveolar macrophages toward tertiary butoxycarbonyl-phe-ala-ala-phe-paraaminobenzoate was inhibited with L-3-carboxy-trans-2,3-epoxypropionyl-leucylamido-(4-guanido)butane, a specific inhibitor of cysteine proteinases, a finding of interest because in general enzymes in this class show little activity at neutral pH. Alveolar macrophages contain EC 3.4.24.11 and EC 3.4.24.15 and there are significant differences among species in enzyme levels within these cells. Alveolar macrophages may participate in the metabolism of bioactive peptides in vivo through the activities of these two enzymes.