Pyruvate kinase from cytosolic fractions of the Ehrlich ascites tumour, normal mouse liver and skeletal muscle.

Comparative studies on cytosolic pyruvate kinase (PK, EC 2.7.1.40) from the Ehrlich ascites tumour, mouse liver and skeletal muscle, revealed the presence of two pyruvate kinase fractions: fraction A, salted out by ammonium sulphate between 21-30% saturation and predominant in the liver (type L); fraction B, salted out between 51-60% saturation and predominant in the tumour (type M2) or skeletal muscle (type M). The sigmoidal kinetics revealed in liver pyruvate kinase only were reconstructed in the mixture of both liver fractions A and B and characterized separately with linear kinetics in a double-reciprocal plot. L-Cysteine inhibited the neoplastic fraction B of pyruvate kinase only by decreasing its Vmax and increasing the Km values in relation to 2-phosphoenolpyruvate. Stearic acid altered kinetic parameters of both fractions A and B of pyruvate kinase from the muscle and liver, but not from the tumour. This suggests that tumours contain a pyruvate kinase variant, characterized by a greater affinity to 2-phosphoenolpyruvate as the main substrate and by a different sensitivity to low-molecular effectors, in comparison with types L, M or M2 of pyruvate kinase from normal tissues.