A series of transplanted mouse and rat tumors was assayed for their content of citric acid cycle and related enzymes, and the results were compared with a representative series of normal tissues. Lactic, malic, and isocitric dehydrogenases, fumarase, oxalacetic carboxylase, and the “condensing” enzyme were found present in tumors in amounts comparable to those in normal tissues. Aconitase and α-ketoglutarate dehydrogenase were present in tumors but to lower extents than in normal tissues. The results warrant the conclusion that neoplastic tissues possess the enzymatic equipment for the citric acid cycle.

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This work was aided by grants from the American Cancer Society, on recommendation by the Committee on Growth of the National Research Council; the National Cancer Institute of the National Institute of Health, Public Health Service; and the U.S. Atomic Energy Commission, Contract No. AT(30-1)777.

A preliminary report of a portion of this work has appeared (36).

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