Crystallization, Characterization and Metabolic Regulation of Two Types of Pyruvate Kinase Isolated from Rat Tissues*

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Abstract
1. 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.