Extraordinarily stable disulfide-linked homodimer of human growth hormone.

Although a 22-kDa human growth hormone (hGH) is the predicted protein product of the hGH-N gene, a pleiotropic collection of uncharacterized molecular weight and charge isoforms is also produced. Using chromatography and preparative SDS-PAGE under reducing conditions we isolated an unusually stable mercaptoethanol-resistant (MER) 45-kDa hGH. A 5-h incubation at 100 degrees C in the presence of 2-mercaptoethanol was required to convert approximately 90% of MER-45-kDa hGH into a 22-kDa hGH.