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A seasonal change was observed in the total level of pyruvate kinase EC 2.7. 1.40 in rats fed on laboratory chow or a high carbohydrate diet. 2. Two types of pyruvate kinase were identified by electrophoresis and an immunological procedure, and named type L and type M. Both types were purified extensively and were isolated as crystals. The molecular weights of type M and type L were 250,000 and 208,300 respectively. 3. No cross immunological reaction was observed between the two types. The antibody for type M was used in estimating the levels of the two types of enzyme in tissue extracts. 4. The level of type L varied greatly under various physiological conditions, whereas that of type M changed only slightly. In alloxan diabetic animals and those fed on a high protein diet or fasted for 48 hours, the total level of pyruvate kinase as well as the ratio of type L to type M decreased greatly, and on subsequent insulin administration and administration of a normal diet, respectively, the level returned to normal. 5. The level of type M increased markedly in regenerating liver and was the only type found in ascites hepatoma cells. 6. Type M was present in muscle, brain, heart, liver, kidney, fat pads and leucocytes, and type L was only present in liver and erythrocytes. 7. The kinetic properties of type M and type L1 were quite different. The apparent K of type L1 for phosphoenolpyruvic acid was about 10 times that of type M, and with type L, the substrate seemed to act as an activator. The sensitivities of type L to inhibition by ATP and p-chloromercuribenzoic acid were also very much higher than that of type M. 8. The physiological significances of the two types of pyruvate kinase were discussed.
Tanaka et al. (Sat,) studied this question.