Isolation and biological characterization of fragments of human growth hormone produced by digestion with plasmin.

The biologically active component of plasmin digested human growth hormone consisted of residues 1-134 attached to residues 141-191 by the disulfide bond between residues 53 and 165. This large fragment of the hormone retained the in vivo capacity to stimulate weight gain and cartilage metabolism in hypophysectomized rats and exhibited the diabetogenic property of the native hormone in partially pancreatectomized, dexamethasone-treated rats. This fragment also retained the in vitro ability to stimulate protein synthesis and amino acid and sugar transport into isolated diaphragm muscle of hypophysectomized rats, Furthermore, a smaller peptide (residues 1-134) derived from the large fragment by reduction and carbamidomethylation of the disulfide bond retained high activity in in vitro systems and the in vivo capacity to stimulate cartilage metabolism provided the peptide was injected intravenously. Thus the present studies demonstrate that many of the in vivo and in vitro metabolic effects of human growth hormone on tissues of hypophysectomized rats can be elicited with a peptide comprising the aminoterminal 134 amino acid residues of native human growth hormone.