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The Enzymology of the Formation and Interconversion of Labile 1-Carbon Groups in Five Hepatomas and in Walker Tumor 256¹

Institut du Cancer de Montréal, Hôpital Notre-Dame, and Département de Biochimie, Université de Montréal, Montréal, Québec, Canada [R. L., L. A. P., M. C. P.], and Department of Biochemistry, Howard University, Washington, D. C. 20001 [H. P. M.]

The levels of the enzymes histidase, urocanase, formiminoglutamic acid transferase, dihydrofolate reductase, serine hydroxymethylase, N^5,10-methylenetetrahydrofolate dehydrogenase, and formylase, all involved in the metabolism of 1-carbon and related compounds, were determined in the cytoplasmic fractions of 5 rat hepatomas, Walker tumor 256, and livers of tumor-bearing rats. The hepatomas studied included the Novikoff, H-35, and Morris 7800, 7777, and 5123D hepatomas. The activities of virtually all enzymes studied were significantly decreased in hepatomas in comparison to corresponding activities in livers of tumor-bearing rats. The hepatoma levels of formiminoglutamic acid transferase and serine hydroxymethylase never exceeded 7 and 41%, respectively, the corresponding enzyme levels found in host liver. The levels of histidase, urocanase, and dihydrofolate reductase were also significantly lower in all hepatomas studied than in livers of tumor-bearing rats. The levels of formylase in the 5123D hepatoma and of N^5,10-methylenetetrahydrofolate dehydrogenase in hepatoma H-35 were found to be comparable to the corresponding enzyme level in livers of tumor-bearing rats; in all other hepatomas studied, however, the levels of these two enzymes were lower than in the host livers. With the exception of serine hydroxymethylase, the activities of all enzymes studied were similar in the two rapidly growing tumors, the Novikoff hepatoma and Walker carcinosarcoma 256. No other correlations could be observed between the growth rates of tumors studied and the levels of any enzymes investigated. The results are consistent with an overall decrease in both the 1-carbon and tetrahydrofolate moieties of the labile 1-carbon pool of tumors and with a decreased interconversion of the metabolically labile formyl and hydroxymethyl groups.

¹ This research was supported by grants from the National Cancer Institute of Canada, The Conseil de la Recherche Médicale du Québec, and USPHS Grant CA 10729.

² Present address: National Cancer Institute, NIH, Bethesda, Md. 20014.

Received 6/10/71. Accepted 2/18/72.