In vitro biosynthesis and chemical characterization of beta-lipotropin, gamma-lipotropin, and beta-endorphin in rat pars intermedia.

Abstract
Three 3 h incubations of pars intermedia cells from 40 rat pituitaries with [35S]methionine, [3H]lysine and [3H]leucine sufficed for the identification and chemical characterization of biosynthesized .beta.-lipotropin, .gamma.-lipotropin and .beta.-endorphin. From the MW, migration on polyacrylamide gels, and sequence Met5, Lys9, Leu14,17, rat .beta.-endorphin was identical to its sheep homologue and no trace of Leu5 .beta.-endorphin could be detected. Rat .beta.-lipotropin differs from that of sheep in its elution properties on CM-cellulose, and its sequence shows Leu2,10,14, Lys20. Rat .gamma.-lipotropin shows the same NH2-terminal sequence as .beta.-lipotropin and is again different from its sheep homologue. The identification of rat .beta.-lipotropin was confirmed by its elective cleavage into .beta.-endorphin after trypsin digestion of the citraconylated peptide, a property not observed with rat .gamma.-lipotropin.