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Inability of 4-Dimethylaminoazobenzene To Act as a Major Source of Labile Methyl Groups^*

E. C. Miller, J. C. MacDonald and J. A. Miller

( McArdle Memorial Laboratory, Medical School, University of Wisconsin, Madison, Wis.)

Weanling rats were fed 4-dimethylaminoazobenzene-N-methyl-C¹⁴ in a diet low in labile methyl groups with and without choline supplements. After 11–13 weeks, only a low percentage of the methyl groups of the liver choline was derived from the methyl groups of the dye in these rats. Thus, under these conditions 4-dimethylaminoazobenzene cannot serve as a major source of labile methyl groups in the rat. At best this dye appears to be a minor secondary source of these groups through oxidative demethylation to one-carbon precursors used in the synthesis of methyl groups in vivo.

Weanling rats fed a diet low in labile methyl groups were only partially protected against the development of kidney hemorrhages by levels of 4-dimethylaminoazobenzene equimethyl to protective levels of choline. Similar levels of 4-dimethylaminoazobenzene and N,N-diethyl-p-phenylene diamine completely protected the rats against the formation of the renal lesions. Restriction of food intake was at least partially responsible for some of these effects. Similarly, 4-aminoazobenzene produced as large an increase as 4-dimethylaminoazobenzene in the leukocyte count of rats maintained on a diet low in labile methyl groups. Thus, neither of these biological systems is a reliable assay for the presence of labile methyl groups in these compounds.

^* This investigation was supported by Grant C355 of the National Cancer Institute, United States Public Health Service, Institutional Grant 71 from the American Cancer Society, and an institutional grant from the Alexander and Margaret Stewart Trust Fund. A gift of crystalline B vitamins from Dr. N. S. Ritter of Merck and Company is gratefully acknowledged.

Present address: Department of Biochemistry, Oxford University.

Received 2/10/55.