Characterization of pro-opiocortin, a precursor to opioid peptides and corticotropin.

Abstract
The high MW (approximately 30,000) precursor to opioid activity (pro-opiocortin) previously detected in extracts of rat pituitary was digested with trypsin, and the resulting peptide mixture was resolved by high-performance reverse-phase chromatography. A peak of opioid activity was eluted at the position of the nonapeptide .beta.-LPH [.beta.-liptotropin] (61-69), which was also the same fragment obtained by trypsin digestion of .beta.s-lipotropin or .beta.-endorphin. This identified the protein as a precursor to the endorphins and Met-enkephalin. No activity was detected in the position corresponding to the Leu5 analog of .beta.s-LPH (61-69), thus ruling out the possibility of a .beta.-lipotropin-liek precursor to Leu-enkephalin in pituitary extracts. Proopiocortin and .beta.-lipotropin are present in rat pituitary extracts in comparable amounts, approximately 10 pmol/mg of tissue.

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