Isolation and Characterization of Fragments of Reduced andS-Carbamidomethylated Human Growth Hormone Produced by Plasmin Digestion. II. Biological and Immunological ActivitiesEndocrinology102:*

Abstract

Noncovalent complexes of peptide fragments, as well as individual fragments, isolated from digests of reduced and S-carbamidomethylated human GH (hGH) produced with human plasmin were studied for biological and immunological activity. Non-covalent complexes of peptide 1-134 and peptide 141-191 and a complex containing approximately equal proportions of peptide 1-134 and peptide 42-134 bound to peptide 141-191 retained 50-100% of the ability of hGH to promote growth and stimulate cartilage metabolism when injected into hypophysectomized rats, to induce N-acetyllactosamine synthetase in mammary tissue explants from pregnant mice, and to stimulate the in vitro oxidation of glucose by isolated adipose tissue from hypophysectomized rats. In contrast to previous findings with covalent complexes containing peptide 1-134, the noncovalent complexes showed only 20-50% of the insulin-like activity of native hGH. The noncovalent complex, 1-134:141-191, exhibited more than twice the lactogenic potency of native hGH. All of the noncovalent complexes gave displacement curves that were essentially indistinguishable from that of native hGH in tests of immunoreactivity. Peptide 1-134, isolated from 1 of the noncovalent complexes by rather drastic procedures, still retained a low order of biological and immunological activity. A peptide comprising residues 20-41 of hGH isolated from the digests proved to have no activity in any test. Another peptide comprising residues 95-134 of hGH had 2-10% of the biological activity of HGH, similar to the low order of activity observed by Sonenberg and his colleagues with the comparable peptide produced from bovine GH. Although as observed in earlier work, peptide 1-134 of hGH by itself posses significant partial growth-promoting and thymidine uptake activity, association with part or all of peptide 141-191 of hGH is required to realize fully the biological activity inherent in the N-terminal peptide.