The purification and characterization of rat placental lactogen

A method has been developed for the purification of rat placental lactogen employing a specific radioreceptor assay (RRA). The method involves precipitation with ammonium sulfate, gel filtration on Sephadex G-100, ion-exchange chromatography on DEAE-cellulose and CM-Sephadex, and preparative isoelectric focusing. The isolation precedure results in a 1300-fold purification and a 10% yield of rat placental lactogen. Potency estimates by RRA indicate that the purified hormone is 41% as active as the ovine prolactin standard (25 I U/mg), but 169% as active as the NIH human placental lactogen preparation. Polyacrylamide gel electrophoresis at pH 8.9 annd analytical isoelectric focusing of the rat placental lactogen reveal 2 major and 2 minor components, all of which are active in the RRA.