Malic dehydrogenase and

Karlsson, B. W., and G. B. Larsson. 1971. Lactic and malic dehydrogenases and their multiple molecular forms in the Mongolian gerbil as compared with the rat, mouse and rabbit. Comparative Biochemistry and Physiology 40B 93-108. 

Various relationships between enzymes of the Krebs cycle and mitochondria are possible. For instance, all enzymes could be enclosed within mitochondrial structures or the enzymes could take part in the structural build-up of the cell. There is no evidence demonstrating that all enzymes of the Krebs cycle are part of the mitochondria. The existence of enzymes with multiple catalytic properties (isocitric dehydrogenase, aconitase, and malic dehydrogenase) and the failure to separate the multiple steps of an overall reaction (pyruvic and a-ketoglutarate oxidation) are sometimes taken as evidence for the participation of the enzyme in the building-up of the mitochondrial structure, but these arguments do not take into account the limitations of the actual biochemical methods, and, therefore, conclusions based upon them are premature. 

In spite of the absence of integral mitochondria, the red cell contains some of the enzymes (fumerase, isocitric dehydrogenase, malic dehydrogenase, and cytochrome oxidase) functioning in the Krebs cycle and electron transport. These enzymes probably represent mitochondrial remnants, and their presence in the mature erythrocyte may be a consequence of their greater stability. Similarly, enzymes concerned with... 

The Oxaloacetic System (Szent-Gyoi i, 1937).— The wide distribution of the three enzymes, succinic and malic dehydrogenase, and fumarase, si ests that they and their respective substrates participate in many tissue respirations. Addition of malonic acid, which inhibits succinic acid oxidation, leads to an almost complete... 

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