Purification and Properties of an Aminopeptidase From Kidney Cellular Particulates

It has long been known that aqueous homogenates of animal tissues are capable of hydrolyzing peptides containing not only L-but, also n-amino acid (2-5) and (Y ,&dehydroamino acid (6) residues.An earlier report from this Laboratory on the distribution of the hydrolytic activities in a wide variety of rat tissues toward glycyl-L-alanine, glycyl-n-alanine, and glycyldehydroalanine showed that the greater part of the activity toward glycyl-L-alanine was always in the soluble fraction of the tissues, whereas most of the activity toward glycyl-n-ala&e was always in the insoluble fraction.The greater part, of the activity toward glycyldehydroalanine was in the soluble fraction of all the tissues studied except that of the kidney, in which it was found in the insoluble, particulate fraction (7).It was considered of interest to study further the peptidase system associated with the particulate fraction of the hog kidney.The enzyme was solubilized by the butanol procedure of Morton (8), and a considerable concentration in activity toward glycyl-n-alanine was achieved by only a few fractionation steps.The activity of the freshly prepared enzyme was at, least 600 times that of the homogenate.Because of the curious property of the enzyme preparation of increasing in activity on storage, it was difficult, to express the actual degree of purification.The purified peptidase, possessing a high degree of physical homogeneity, was found to effect, the hydrolysis at a high rate, not only of a wide variety of peptides containing n-amino acids in the terminal position but also, and at similarly high rates, of the corresponding peptides containing L-and dehydroamino acids.The interesting question of the substrate and optical specificity of the enzyme system has therefore been considered in some detail with 65 substrates.Additional studies on metal activation, kinetics, and molecular properties have served for further characterization.