In vivo and in vitro studies on the pathway of modification of mussel pyruvate kinase.

1. On aerial exposure, pyruvate kinase is inactivated in various organs of M. edulis; the decrease of activity is slower in muscle than in non-muscular tissue. 2. Anoxic in vitro incubation of gills results in a rapid inactivation of pyruvate kinase. No change occurs in an aerated medium. 3. Enzyme inactivation is mimicked in part by oxic incubation in an acidified medium containing 5,5-dimethyloxazolidine-2,4-dione, and by the action of calcium ionophore A23187. 4. Incubation of supernatant of gill homogenate results in a slow inactivation of pyruvate kinase that is inhibited by trifluoperazine or EGTA and stimulated by exogenous calmodulin. 5. Addition of ATP plus cAMP stimulates pyruvate kinase inactivation in supernatant of homogenized muscle but not so in a high molecular weight fraction thereof.