Hydrolysis of some cystine amniopeptidase and aminopeptidase substrates by human placental enzymes after isoelectric focusing.

Several cystine aminopeptidase- and aminopeptidaselike activities of mature human placenta were demonstrated by chromatography on CM-Sephadex and subsequent preparative flat bed isoelectric focusing. Enzyme tests were carried out by using a micro modification of the Bratton-Marshall reaction with seven amino acid-rho-nitroanilides and one amino acid beta-naphthylamide as substrates. By this method three main activities were detected; each was nonhomogeneous and capable of hydrolyzing cystine aminopeptidase- as well as aminopeptidase substrates. The substrates benzyl-cystine-rho-nitroanilide, cystine di-rho-nitro-anilide and cystine di-beta-naphthylamide were split by different enzymes. By studying the effects of several effectors or of heating, no enzyme with the properties described in the literature for serum cystine aminopeptidase could be unequivocally demonstrated. The results report here suggest that serum cystine aminopeptidase--in contrast to placenta cystine aminopeptidase--is either altered severely in its structure or that it represents a multiplicity of enzymes, which attack "specific" substrates and are therefore jointly manifested as cystine aminopeptidase.