Identification of a nonimmunoreactive but highly bioactive form of prolactin in the mouse pituitary by gel electrophoresis.

Polyacrylamide gel electrophoresis of fresh mouse pituitary extracts in 10% acrylamide reveals three closely situated bands of protein in the area where prolactin usually migrates. The fastest migrating band constitutes only 10–30% of the total, but it is twice as active in the pigeon crop-sac bioassay as the major band and has little or no immunologic cross-reactivity against an antiserum to the major constituent. This newly recognized band may be a hitherto unrecognized molecular variant of prolactin.