The 20,000 molecular weight variant of human growth hormone. Preparation and some physical and chemical properties.

Extracts of frozen human pituitary glands contain, in addition to normal growth hormone (hGH (Mr = 22,005), a variant of lower molecular weight (approximately 20,000) (Singh, R. N. P., Seavey, B. K. and Lewis, U. J. (1974) Endocrinol. Res. Commun. 1, 449-464). This material, designated 20K hGH, occurs in various forms with the majority present as a heterologous dimer of Mr = 20,000 hGH and hGH. The purification scheme for obtaining the variant from these fractions is described. Analysis of Mr = 20,000 hGH in the sequenator has confirmed that residues 32-46 of hGH are absent in Mr = 20,000 hGH. The structures of hGH and Mr = 20,000 hGH have been compared by 1H nuclear magnetic resonance spectroscopy, circular dichroism, spectrophotometric titration, and nitration of the tyrosine residues by tetranitromethane. The results indicate that the folding of the polypeptide chain of the two proteins is similar but not identical.