PARTIAL HYDROLYSIS OF BOVINE PARATHYROID HORMONE BY DILUTE ACID AND PROTEOLYTIC ENZYMES: EFFECTS ON IMMUNOLOGICAL AND BIOLOGICAL ACTIVITIES.

Abstract

Phenol-extracted bovine parathyroid hormone was partially hydrolyzed with hot dilute HC1 and with trypsin, chymotrypsin and carboxypeptidase A. The effects of each treatment on the immunological and biological activities and on the electrophoretic mobility of the hormone were measured by quantitative complement fixation and complement fixation inhibition, by the calciummobilization assay method of Munson, and by vertical starch gel electrophoresis. Hydrolysis of the hormone with hot 0.2N HC1 did not alter the biological activity despite changes in the structure of the hormone shown immunochemically and by electrophoresis. These results indicate that the entire polypeptide chain is not essential for full calcium-mobilizing activity in the rat. Digestion of the hormone with trypsin was rapid and produced peptide fragments that were devoid of antigenic or biological activities. Chymotryptic digestion was less marked, substantially decreasing, but not eliminating, the immunological and biological activities. Neither the biological activity nor the electrophoretic mobility of the polypeptide chain was altered following removal of a COOH-terminal fragment by carboxypeptidase A. However, the COOH-terminal portion of the molecule contributed to the immunological activity of the hormone, as shown by a decrease in the amount of complement fixed at optimal antigen concentration. (Endocrinology76: 979, 1965)