A systematic study of the carbohydrate-metabolizing enzyme systems of the Morris hepatoma 5123 was carried out, and results were interpreted in the light of normal liver data and in comparison with previously established values of Novikoff hepatoma.

The cellularity of the Morris tumor was in the same range, whereas the nitrogen content of the average cell was significantly decreased, as compared with that of the control liver.

In the average Morris hepatoma cell glucose-6-phosphatase (56 per cent), phosphohexoseisomerase (66 per cent), lactic dehydrogenase (65 per cent), and 6-phosphogluconate dehydrogenase (50 per cent) decreased to the same extent as the nitrogen level (58 per cent). On the other hand, in relation to the decreased nitrogen content glucose-6-phosphate dehydrogenase activity was preferentially maintained in normal range, whereas phosphoglucomutase (15 per cent) and fructose-1,6-diphosphatase (30 per cent) were preferentially depleted.

A comparison of these enzymes in the two examined liver tumors of differing growth rates showed that the marked increase in glucose-6-phosphate dehydrogenase activity in the Novikoff tumor was not present in the Morris hepatoma. However, another enzymatic lesion of the Novikoff hepatoma (markedly decreased phosphoglucomutase) occurred in Morris hepatoma to a similar extent. On the other hand, some of the enzymes missing in the Novikoff tumor (glucose-6-phosphatase, fructose-1,6-diphosphatase) were present but in diminished activity, manifesting only a partial lesion in gluconeogenesis in the Morris hepatoma.

It appears that the extent of the examined enzymatic lesions may be correlated roughly with the growth rates of the Morris and Novikoff hepatomas.

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This work was supported in part by grants from the Damon Runyon Memorial Fund for Cancer Research, Inc. (DRG-542), American Cancer Society (No. E-254), and National Cancer Institute, National Institutes of Health, U.S. Public Health Service (CY-5034).

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