PLASMA MEMBRANE-BOUND AND LYSOSOMAL PEPTIDASES IN HUMAN ALVEOLAR MACROPHAGES

Alveolar macrophages protect the lungs against noxious agents. Proteas es and peptidases are essential for this defense and many metabolic ac tivities. Human alveolar macrophages were evaluated for the presence o f six important peptidases. Deamidase, a serine peptidase identical wi th the lysosomal protective protein and possibly with cathepsin A, had high specific activity in alveolar macrophages and is also present in cultured mouse J774A.1 and human U937 cells, used for the sake of com parison. In fractionated J774A cells, most of the deamidase activity w as in the lysosomal fraction and in the final supernatant. Deamidase i n human alveolar macrophages, obtained by bronchoalveolar lavage from 23 patients, cleaved dansyl-Phe-Leu-Arg at a rate of 2.26 mu mol/h/mg protein and hydrolyzed the chemotactic peptide N-f-Met-Leu-Phe even fa ster, at a rate of 53.1 mu mol/h/mg protein, the highest activity for this enzyme with any of the cells we tested. Rabbit antiserum, elicite d with the recombinant partial sequence of the enzyme, immunoprecipita ted 77-88% of the macrophage deamidase. In immunocytochemistry, this a ntiserum localized deamidase within the human macrophages. The enzyme was inhibited by diisopropylfluorophosphate (DFP; 1 mM) and by ebelact one B (10 mu M), noncompetitively. The mRNA of deamidase was detected in mouse macrophages by Northern blot; the two protein chains of deami dase were shown in human macrophages by Western blot. In addition, two other serine peptidases were also highly active in macrophages: dipep tidyl peptidase IV (1.38 mu mol/h/mg protein) and prolylcarboxypeptida se (0.72 mu mol/h/mg protein). The activity of plasma membrane zinc me tallopeptidases, neutral endopeptidase 24.11 and carboxypeptidase M, i n contrast, was low or absent (angiotensin I converting enzyme; kinina se II). Thus, highly active serine peptidases are present in human mac rophages, and deamidase seems to be the relatively most active one.