Vol. 26, No. 3, 1967 A MONOMERIC FORM OF PROCARBOXWEPTIDASE A FROM THE SPINY PACIFIC DOGFISH* Andras G. Lacko and Hans Neurath Department of Biochemistry, University of Washington Seattle, Washington 98105 Received December 19, 1966 INTRODUCTION Although the activation of trypsinogens and chymotrypsinogens from various species has been extensively studied (Neurath, 1964), only limited information is available on the mechanism of activation of procarboxypeptidases. The activation of bovine procarboxypeptidase A (PCPA) is complicated by the tri- and dimeric aggregates in which this zymogen occurs (Brown et al., 1963). Folk and Schirmer (1965) have suggested that porcine PCPA may occur in the monomeric form but no data have yet been reported on the isolation and purifi- cation of such a zymogen. In this preliminary communication, we should like to report the purifica- tion and partial characterization of a monomeric form of PCPAisolated from the Spiny Pacific Dogfish. This tissue is known to contain the samekind of proteolytic enzymes, in the zymogen form, which are characteristic of the bovine pancreas (Prahl and Neurath, 1966 a,b). Apart from possible phylogenetic implications, the isolation of dogfish PCPA provides an excellent system for studying the mechanism of activation of the eymogen precursor of carboxypepti- dase A. EXPERIMENTAL Dogfish pancreas glands were obtained from commercial fishermen in the Puget Sound area and processed according to Prahl and Neurath (1966 a), to ob- *This work has been supported by the National Institutes of Health (GM 01;617), The American Cancer Society (P-79), and the Office of Naval Research, Depart- ment of the Navy (NONR 477(35)). 272