Biosynthesis of beta-endorphin from beta-lipotropin and a larger molecular weight precursor in rat pars intermedia.

Abstract

When isolated rat pars intermedia cells were incubated for 10 min with radioactive amino acids, 1 major labeled protein with a MW of 30,000 .+-. 1500 was extracted. This protein contained in its sequence the antigenic determinants for corticotropin and .beta.-melanotropin by immunoprecipitation. When the radioactivity incorporated into this large MW protein during the first 10 min was chased by a further incubation in presence of an excess of unlabeled amino acid, the initial protein was degraded into several smaller peptides including .beta.-endorphin and .beta.-lipotropin. Another 18,000 dalton peptide was also observed and was tentatively identified as a larger molecular form of corticotropin. From the kinetics of the maturation of the initial precursor, it was concluded that the initial cleavage of the 30,000 dalton peptide gives rise to .beta.-lipotropin and the 18,000 dalton form of corticotropin. .beta.-Lipotropin is subsequently cleaved to form .beta.-endorphin.