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M Lumb, I Chanarin, J Perry and R Deacon
The metabolism of the methyl group of 5-methyltetrahydrofolate was studied
in rats in which cobalamin had been inactivated by exposure to nitrous
oxide and in air-breathing control animals. Methylfolate labeled with [14C]
in the methyl group and with [3H] in the pteridine- PABA portion was
injected and the disappearance of [14C]H3- relative to [3H]folate was
measured in liver. The half-time of the methyl group in the livers of
control rats was two hours. There was no turnover of the methyl group for
the first 72 hours after cobalamin inactivation. After 72 hours, there was
a slow turnover of the methyl group, with a half- time of 43 hours. In
control rats, it is assumed that the methyl group was metabolized by
transfer to homocysteine to form methionine. In cobalamin-inactivated rats,
it was shown that methylfolate was used as the substrate for forming folate
polyglutamate, and analogues with 3, 4, and 5 glutamic acid residues were
present. It is likely that oxidation of the methyl group by methylene
tetrahydrofolate reductase occurs from folate polyglutamate containing six
and seven glutamic acid residues, (Brody et al, Biochemistry 21: 276,
1982), since we were unable to demonstrate labeled methyl in longer chain
analogues.
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| Copyright © 1985 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||
