Plasma carboxypeptidase N, subunits and characteristics

Abstract

Subunits of human plasma carboxypeptidase N, the enzyme that cleaves kinins and anaphylatoxins, were separated in gel filtration and in disc gel electrophoresis. During storage, the activity of the separated heavy ( M r 98,000) and light ( M r 42,000) subunits increased, while the native enzyme disappeared. Carboxypeptidase N is more stable at 37 °C in native than in dissociated form. A carboxypeptidase having about the same molecular weight as the light subunit of human plasma enzyme was purified from homogenized hog liver by using affinity chromatography. Affinity chromatography was also applied to concentrate a carboxypeptidase from hog plasma. The substrate specificity of human carboxypeptidase N was studied with 12 peptide and 1 ester substrates. Although carboxypeptidase N cleaved C-terminal lysine faster than arginine, alanine in the penultimate position increased the rate of hydrolysis of C-terminal arginine.