1-Serines, isotopically labelled, synthesis

The (9-carbon of serine as well as the a-carbon of glycine were extensively incorporated into the methyl group of thymine in the adult rat (334). In addition, formate-C served as a precursor of the methyl group of thymine both in vivo (29) and in vitro (335) formaldehyde was also utilized for thymine methyl group synthesis (336). Isotopic data indicated that the hydroxymethyl group of serine, doubly labeled with and D, was transferred to position 5 of thymine with a minimum of 1.5 atoms of D per carbon atom this demonstrated that the /3-carbon of serine was not metabolized all the way to formate (337),... 

Cheung, Y., and C. Walsh Stereospecific Synthesis of Isotopically Labeled Serine at Carbon 3 and Stereochemical Analysis of D-Serine Dehydrase Reaction. J. Amer. Chem. Soc. 98, 3397 (1976). 

Similar studies designed to measure the turnover of cerebrosides of brain tissue have been carried out by a number of investigators. Davison et al. (1959) employed serine-3-to label brain cerebrosides and computed the turnover rate to be near 200 days. On the other hand Hajra and Rad in (1964) administered acetate-and measured the rate of loss of radioactivity from the fatty acid moieties of the cerebrosides. In the latter experiments the half-time was near 42 days. When the hexose of the cerebrosides is labeled by means of glucose-1- C or galactose-1- C, the rate of depletion of the isotope indicated a half-time of near 40 days (Burton, et al, 19 ). These data indicate that cerebrosides turn over slowly in brain, at a rate near 40 days, as measured by the hexose and fatty acid moieties. The data derived from the serine experiment undoubtedly indicates that the sphingosine pool in brain is small and that this compound is reused in the synthesis of the sphingolipids. 

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