Demonstration of beta-lipotropin activating enzyme in porcine pituitary.

Porcine β-lipotropin was incubated with a crude porcine pituitary homogenate, and the main cleavage products of the hormone were isolated and identified. Our results gave evidence for the enzymic cleavage of the Lys⁴⁶-Met⁴⁷, Arg⁶⁰-Tyr⁶¹, Leu⁷⁷-Phe⁷⁸, and Lys⁷⁹-Asn⁸⁰ bonds of the β-lipotropin structure. The cleavage of the Arg⁶⁰-Tyr⁶¹ peptide bond was accompanied with the concomitant release of opiate activity in the first period of incubation, provided that bacitracin was present in the incubation mixture. The enzyme was differentiated from trypsin or plasmin and appears to be a specific intracellular protease involved in the biosynthesis of pituitary endorphins.