Abstract
Highly purified calf brain cathepsin D (EC 3.4.23.5) selectively splits the Leu77-Phe78 and Ala36-Ala37 peptide bonds of human .beta.-lipotropin. The formation of human .beta.-melanotropin from .gamma.-lipotropin, and that of .gamma.-endorphin from .beta.-endorphin, may be due to the action of cathepsin D during isolation procedures.