The levels of the enzymes glucose-6-phosphate dehydrogenase and threonine dehydrase were determined in a series of “minimal-deviation hepatomas,” and the results were compared with the levels of these same enzymes attainable in normal liver under various dietary and hormonal conditions. It was noted that in normal liver there appeared to be a reciprocal relationship between the glucose-6-phosphate dehydrogenase and threonine dehydrase—i.e., both enzymes could not be induced to high levels at the same time. The studies on hepatomas also revealed a wide range of values for these enzymes, with some tumors having relatively high levels of threonine dehydrase with low levels of glucose-6-phosphate dehydrogenase, and some having a high glucose-6-phosphate with a low threonine dehydrase. One tumor did have fairly high levels of both enzymes after the host animal was fed a high protein diet.

It is felt that these results suggest that the hepatomas thus far studied make up a spectrum of tumors with enzyme levels varying within the range that can be found in normal liver under certain dietary and hormonal conditions. It is also suggested that the control of these enzymes is defective in that the adjustments which the cancer cell can make to changes in substrate level differ markedly from the adjustments the normal liver cell can make.

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This work was supported in part by a grant (C-646) from the National Cancer Institute, National Institutes of Health, U.S. Public Health Service.

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