Purification and partial characterization of prolactin from the California ground squirrel (Spermophilus beecheyi).

Prolactin (Prl) secreted by cultured ground squirrel (Spermophilus beecheyi) pituitaries (SbPrl) was purified by gel filtration on Sephadex G-100 and ion-exchange chromatography on Polybuffer Exchanger 94. Purification from culture medium from 190 pituitaries yielded 1.1 mg of purified SbPrl. The SbPrl has an apparent molecular weight of 27,000 by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, an isoelectric point of 6.3, and does not contain any asparagine-linked carbohydrate. Purified SbPrl displaces 125I-labeled ovine Prl from binding sites on lactating rabbit mammary gland membranes and stimulates secretion of alpha-lactalbumin by cultured mouse mammary gland epithelial cells.