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The anterior pituitary gland produces a 20-kilodalton (kDa) variant of human growth hormone (hGH) that differs from the predominant 22-kDa form of hGH in that amino acid residues 32-46 are deleted. Previous work has suggested that the 20-kDa variant possesses the full growth-promoting and lactogenic activities of 22-kDa hGH but lacks its intrinsic diabetogenic and insulin-like activities. In the present study, recombinant DNA techniques were used to prepare biosynthetic 20-kDa hGH, and some of the biological properties of the purified hGH variant were examined. The biosynthetic 20-kDa hGH variant was found to share the propensity for aggregation exhibited by its native counterpart. Moreover, like the native variant, biosynthetic 20-kDa hGH possessed full growth-promoting activity in the weight gain test in hypophysectomized rats. However, contrary to previous work suggesting that native 20-kDa hGH lacks diabetogenic and insulin-like activities, biosynthetic 20-kDa hGH was found to have substantial diabetogenic activity when administered chronically to ob/ob mice and to possess approximately 20% the in vitro insulin-like activity of biosynthetic 22-kDa hGH on isolated epididymal adipose tissue of hypophysectomized rats. The diabetogenic and insulin-like activities of biosynthetic 20-kDa hGH cannot be ascribed to contamination of the hormone preparation with the 22-kDa form of hGH or with other diabetogenic or insulin-like pituitary peptides. Therefore, the results strongly suggest that diabetogenic and insulin-like activities are also intrinsic properties of the 20-kDa variant of hGH.A 20-kilodalton variant of human growth hormone (20-kDa hGH) has been isolated from human pituitary glands (1) and has been found to differ from the predominant 22-kilodalton form of hGH (22-kDa hGH) in that residues 32-46 are deleted (2, 3). The variant is produced in the human pituitary, because the nucleotide sequence encoding residues 32-46 is sometimes excised during the processing of hGH pre-mRNA to hGH mRNA (4). As a consequence, approximately 5-10%1 of the hGH present in the human pituitary is 20-kDa hGH (1). Physicochemical studies of 20-kDa hGH (3) suggest that its conformation is similar but not identical to that of 22-kDa hGH.The 20-kDa variant of hGH has been reported (1, 5) to have growth-promoting activity in the hypophysectomized rat equivalent to that of 22-kDa hGH. Moreover, its lactogenic activity in the pigeon crop sac assay equals that of 22-kDa hGH (1). On the other hand, Lewis et al. (5) reported that 20-kDa hGH lacked diabetogenic activity, in that it failed to produce hyperglycemia and glucose intolerance in dogs, when administered 10 hr prior to a glucose tolerance test. Also, this same group reported (6) that 20-kDa hGH lacked the acute insulin-like property of 22-kDa hGH, since the 20-kDa hGH variant failed to produce hypoglycemia and increase plasma free fatty acids when administered to hypophysectomized rats and did not increase glucose uptake or oxidation to CO2 by isolated rat adipose tissue wh...

The gene coding for human growth hormone (hGH) was fused to the coding sequence for the signal peptide of a secreted Escherichia coli protein. STII heat-stable enterotoxin. This hybrid gene was expressed in E. coli. The signal peptide is properly processed and hGH is secreted in to the periplasmic space. In E. coli, some of the material made is proteolytically clipped or deamidated. The effect of culture conditions on the expression and secretion of hGH was studied and several important parameters were identified, including culture temperature and duration, cultivation pH, K+ levels, plasmid structure, and nutrient supplements. Alteration of culture conditions significantly improves the recovery yield and product quality of human growth hormone.

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