Isolation of Internally Labeled Rat Prolactin by Preparative Disc Electrophoresis

Abstract

The preparation of rat prolactin labeled internally with H3- and C14-lysinc is described. The incorporation procedure was carried out by incubating rat pituitary glands in vitro in the presence of the labeled amino acids. Estrogen pretreatment of the animals enhanced the synthesis and release of prolactin by the incubated pttuitaries. Fractionation of the labeled pituitary proteins was performed on a simple preparative disc electrophoresis column capable of separating 10 mg quantities of protein. A large peak of radioactivity which emerged from the column soon after the dye front was shown to be labeled rat prolactin. A much smaller and later peak of radioactive growth hormone was also isolated. The incubation medium was found to contain most of the labeled prolactln formed during the incubation, relatively little prolactin being present in the gland after 20 hr.