In vitro biosynthesis of beta-endorphin in pituitary glands.

Abstract
.beta.-Endorphin is a 31 amino acid polypeptide isolated from the pituitary gland of different species of animals. It has strong morphine-like activity. It is formed of amino acid residues 61-91 of .beta.-lipotropin. Speculation has arisen whether it is biosynthesized in situ or transformed after secretion of .beta.-lipotropin. The present in vitro studies show that it is found as .beta.-endorphin in bovine pituitary slices incubated with radioactive amino acid precursor [35S]methionine. Chemical characterization and microsequencing of a newly biosynthesized material proves its identity with isolated unlabeled .beta.-endorphin and shows that it has a methionine residue at its 5th position, as expected.