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Journal of Nutrition Vol. 81 No. 4 December 1963, pp. 372-378
Copyright © 1963 by American Society for Nutrition
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Vitamin B12 and DNA Biogenesis1

Rogene F. Henderson2 and James S. Dinning

Department of Biochernistry, University of Arkansas School of Medicine, Little Rock, Arkansas

The enzyme, methylene tetrahydrofolic dehydrogenase, which mediates the reduction of one-carbon fragments from the formate to the formaldehyde level in the metabolic pathway leading to thymine methyl biogenesis, is reduced in activity in vitamin B12-deficient chick livers. The addition of vitamin or coenzyme B12 in vitro under aerobic conditions stimulates the deficient enzyme preparations with a Km of 2.9 x 10-10 M. A test of the physiological significance of this stimulation has been made. Control and vitamin B12-deficient chickens were injected with tracer amounts of formate-C14 and formaldehyde-C14. With either tracer the specific activity of the purines and of thymine was diminished in the bone marrow of the deficient chicks, but the percentage decrease in the specific activity of thymine was greater than the percentage decrease in the purines. No difference was observed between the 2 tracers. It is concluded that a form of vitamin B12 plays a significant role in DNA synthesis, probably in the biogenesis of the thymine methyl.

1 This investigation was supported by Research Grant no. A-721 from the National Institutes of Health, United States Public Health Service.

2 Postdoctoral Fellow of the National Cancer Institute, National Institutes of Health.

Manuscript received 5 July 1963.




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