SPECIES SPECIFICITY AND STRUCTURE-FUNCTION RELATIONSHIPS OF GROWTH HORMONE

Abstract

This chapter describes the species specificity and structure–function relationships of growth hormone (GH). GH is a protein hormone derived from the anterior pituitary gland. It comprises a single polypeptide chain of about 190 amino acids, containing two intrachain disulfide bridges. The apparent rapid evolution of GH in the primates makes sequence studies on GH for primates other than man of particular interest. The sequence of GH from the rhesus monkey has been reported. This is very similar to that of human GH, differing at only four residues, suggesting that the rate or evolution of GH because the divergence of old-world monkeys and great apes has been slow. The implication is that GH underwent a period of remarkably rapid evolution early in primate evolution. An alternative explanation is that the primate and nonprimate GH genes are not strictly homologous, implying that a second gene is present in the human genome, homologous with nonprimate GHs and a second gene is present in the nonprimate mammalian genome, homologous with human GH. The situation is complicated by the occurrence of a cluster of GH-like genes in man.