The appearance of a 34,000-dalton inhibitor of calpain (Ca2+-dependent cysteine proteinase) in rat liver after the administration of phenylhydrazine

A 34,000-dalton inhibitor of calpain (Ca2+-dependent cysteine proteinase) was found in the cytosol of anemic rat liver. When phenylhydrazine hydrochloride was continuously administered to rats, a 280,000-dalton calpain inhibitor that existed originally in the liver gradually disappeared within two weeks and, concomitantly, a 34,000-dalton inhibitor appeared. The purified 34,000-dalton inhibitor resembles 280,000-dalton inhibitor in that both are heat-stable proteins and do not inhibit papain and trypsin. Unlike the protomers of a 280,000-dalton inhibitor, 34,000-dalton inhibitor does not show any sign of self-association.