| Abstract: | Methods for selective reduction of the disulfide bonds in ovine prolactin are reported. Cleavage of all three disulfide bonds abolishes biological activity and denatures the hormone. Reduction-carbamidomethylation of one or two of the disulfide bridges does not diminish the biological activities in the pigeon crop-sac and mouse mammary gland bioassays. When compared to the native hormone, monomers of these two partially reduced-carbamidomethylated derivatives also show only modest changes in properties measured by exclusion chromatography, circular dichroism, and immunological cross-reactivities. However, cleavage of cystine-4--11 and cystine-191--199, followed by carbamidomethylation, destroys the biological activity of this derivative in a teleost fish bioassay (Gillichthys urinary bladder). In contrast, reduction of cystine-4--11 actually increased the teleost potency of this derivative compared to the intact hormone. Since teleost prolactin appears to lack a homologue to the cystine-4--11 disulfide bond in the amino-terminal loop of the ovine hormone, selective reduction of this bond in ovine prolactin may produce a derivative whose properties more closely resemble the fish hormone. |
