A NOVEL MAMMALIAN HIGH-MOLECULAR-WEIGHT AMINOPEPTIDASE

Studies with the human lymphoma U937 cell line revealed the presence o f two soluble aminopeptidase activities. Using specific antisera a one of these was identified as the puromycin-specific aminopeptidase, whi le the other appeared to be a novel similar to 200-kDa activity, The k inetic properties of this high-molecular-weight aminopeptidase, referr ed to as Ap(200), were similar to those of the puromycin-sensitive ami nopeptidase, but showed quantitative differences. Ap(200) is relativel y insensitive to inhibition by both puromycin, K-i = 27 mu M and besta tin, K-i = 1.6 mu M. Among the synthetic beta-naphthylamides, Ap(200) is more specific for alanine-beta-naphthylamide compared to the puromy cin-sensitive aminopeptidase. Similarly, this enzyme cleaves a more li mited number of physiological peptides exhibiting a preference for the enkephalins. Ammonium sulfate, but not sodium chloride at the same io nic strength, was able to dissociate the high-molecular-weight aminope ptidase to a similar to 100-kDa active form. The high-molecular-weight aminopeptidase is found as a low abundant protein in a number of tiss ues including intestine, kidney, liver, lung, muscle, spleen and teste s, but could not be detected ill adrenal, heart, or brain. Thus, it ha s a tissue distribution which differs from the puromycin-sensitive ami nopeptidase. (C) 1997 Academic Press.