Regulation of the Concentration or Activity of Pyruvate Kinase in Yeasts and its Relationship to Gluconeogenesis

Marked decreases in the concentration of pyruvate kinase have been observed in certain yeasts grown in conditions of gluconeogenesis (Ruiz-Amil, de Torr6ntegui, Palacian, Catalina & Losada, 1965; Gancedo, 1966). A similar behaviour with low glucose concentration in the medium has also been claimed (Hommes, 1966). Recently Hess, Haeckel & Brand (1966) found a strong activation by FDP* of the pyruvate kinase of brewer's yeast. We now report that two alternative mechanisms for the regulation of pyruvate kinase occur in different yeasts, one controlling its concentration and the other its activity. Either of these regulatory mechanisms permits a 'shutting off' of pyruvate kinase at the level of the phosphoenolpyruvate crossroad in gluconeogenesis.This work was supported by U.S. Public Health Service Research Grant GM08041. J.M. G. and C. G. were aided by Fellowships from the Comisarfa de Protecci6n Escolar, Spain.Peer reviewe