Size heterogeneity of rat pituitary prolactin

Abstract

The occurrence of multiple forms of rat prolactin with different MW (size heterogeneity) was studied with anterior pituitary extracts, purified rat prolactin and 125I-labeled rat prolactin. In each case, 3 main forms of the hormone were detected by gel filtration on Sephadex G-100: a major one (80-90%) corresponding to monomeric prolactin (MW 22,000-25,000), a peak (8-20%) that could be a dimer (MW 45,000-50,000) and a small quantity (1-5%) of a component of much greater MW. On freezing and thawing of 125I-labeled rat prolactin, there was little interconversion of monomer and dimer peaks, but both were converted substantially to very high MW material. All 3 peaks of 125I-labeled rat prolactin could be precipitated by anti-(rat prolactin) serum and all 3 gave similar patterns of radioactive peptides after digestion with chymotrypsin followed by high-voltage paper electrophoresis. On sodium dodecyl sulfate/polyacrylamide-gel electrophoresis, the monomer peak of 125I-labeled prolactin migrated as a single component of MW 22,000, the very high MW peak largely dissociated to a component running in the same position as the monomer, and the dimer peak migrated partly as a component of MW 45,000 and partly as a component migrating with monomeric prolactin. No treatment was found that could dissociate the dimer peak completely to monomeric prolactin.