Enzymatic cleavage of pro-opiomelanocortin by anterior pituitary granules. Evidence for a chymotryptic-like enzyme.

This paper presents the results obtained when pig anterior pituitary granule lysates are incubated with rat pro-opiomelanocortin (POMC). The resultant peptides were analyzed by 3 systems of high-performance liquid chromatography. This approach, when coupled with microsequence analysis of the conversion products, allowed the unambiguous identification of a major chymotryptic-like activity (pH optimum around 8) associated with the granule lysates with a specificity directed towards selective Tyr-X and Phe-X bonds within the POMC molecule. Furthermore, these results also demonstrate that although the detected enzyme activity gives rise to products 'resembling' those expected, the characterization of the 'elusive' maturation enzyme responsible for the cleavage at pairs of basic residues remain to be critically evaluated.