Am. J. Respir. Cell Mol. Biol., Vol 13, No. 2, Aug 1995, 196-204.
Plasma membrane-bound and lysosomal peptidases in human alveolar macrophages
HL Jackman, F Tan, D Schraufnagel, T Dragovic, B Dezso, RP Becker and EG Erdos
Department of Pharmacology, University of Illinois College of Medicine, Chicago 60612, USA.
Alveolar macrophages protect the lungs against noxious agents. Proteases
and peptidases are essential for this defense and many metabolic
activities. Human alveolar macrophages were evaluated for the presence of
six important peptidases. Deamidase, a serine peptidase identical with 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 comparison. In
fractionated J774A cells, most of the deamidase activity was in the
lysosomal fraction and in the final supernatant. Deamidase in human
alveolar macrophages, obtained by bronchoalveolar lavage from 23 patients,
cleaved dansyl-Phe-Leu-Arg at a rate of 2.26 mumol/h/mg protein and
hydrolyzed the chemotactic peptide N-f-Met-Leu-Phe even faster, at a rate
of 53.1 mumol/h/mg protein, the highest activity for this enzyme with any
of the cells we tested. Rabbit antiserum, elicited with the recombinant
partial sequence of the enzyme, immunoprecipitated 77-88% of the macrophage
deamidase. In immunocytochemistry, this antiserum localized deamidase
within the human macrophages. The enzyme was inhibited by
diisopropylfluorophosphate (DFP; 1 mM) and by ebelactone B (10 microM),
noncompetitively. The mRNA of deamidase was detected in mouse macrophages
by Northern blot; the two protein chains of deamidase were shown in human
macrophages by Western blot. In addition, two other serine peptidases were
also highly active in macrophages: dipeptidyl peptidase IV (1.38 mumol/h/mg
protein) and prolylcarboxypeptidase (0.72 mumol/h/mg protein). The activity
of plasma membrane zinc metallopeptidases, neutral endopeptidase 24.11 and
carboxypeptidase M, in contrast, was low or absent (angiotensin I
converting enzyme; kininase II).(ABSTRACT TRUNCATED AT 250 WORDS)
