THE ENZYMATIC HYDROLYSIS OF AMINO ACID β-NAPHTHYLAMIDES II. PARTIAL PURIFICATION AND PROPERTIES OF A PARTICLE-BOUND COBALT-ACTIVATED RAT KIDNEY AMINOPEPTIDASE

Abstract

In order to determine the relationship and characteristics of the soluble and tissue-bound (so-called "lyo" and "desmo") components of enzymes in histochemical and biochemical systems, a biochemical investigation of the hydrolysis of l-leucyl β-naphthylamide in rat kidney was undertaken. By ultracentrifugation, autolysis, salt and solvent fractionation procedures and DEAE-cellulose column chromatography primary soluble and tissuue-bound enzymes were separated and partially purified. The soluble enzyme was found to be inhibited by p-chloromercuribenzoate and reactivated by cysteine. The tissue-bound enzyme was found to be inhibited by o-phenanthroline and reactivated by Co++, and hydrolyzed peptides and amino acid β-naphthylamides at rates differing markedly from those of the soluble enzyme and commercial leucine aminopeptidase. Disc electrophoresis of the tissue-bound enzyme preparation demonstrated two protein bands, both revealing enzymic activity with almost identical hydrolytic characteristics, i.e., isozymes. This evidence established the identity of the tissue-bound Co++-activated enzyme with that found histochemically in the brush border of the proximal tubuli, and indicated its functional capacity as that of an aminopolypeptidase. It was also concluded that in the system investigated the "lyo" and "desmo" components represented, in reality, distinct enzymes with unique characteristics.