The Biogenesis of Choline and Methionine Methyl Groups and of the Serine Hydroxymethyl Group from Intramolecularly Labeled Formaldehyde-14c,d2.

The metabolism in the living rat of formaldehyde, doubly labeled with deuterium and *‘C, was investigated previously in this laboratory (1). In the forementioned studies, the double labeling was accomplished by admixture of two preparations of formaldehyde, one labeled with deuterium, the other with 14C. This type of double labeling has been referred to as intimolecular (3, 4). The results obtained in this earlier investigation indicated that formaldehyde was incorporated into the methyl groups of choline and creatine via an intermediate at the oxidation level of formate, but it was pointed out that interpretation of the results was limited because of the possibility of isotope selection (l-7). A study of the biosynthesis of methyl groups with formate-W ,D as precursor (6) showed that it is possible to minimize, in fact to eliminate, by intramolecular double labeling, the disproportionating effects brought about by hydrogen isotope selection upon the deuterium to 14C ratios that had been observed with i&m&cuZar multiple labeling of compounds with l*C, deuterium, and tritium (2-5, 7). Therefore, in order to arrive at less equivocal results with the doubly labeled formaldehyde, this compound has been prepared with the 1% bonded to deuterium intramolecularly, and the level of oxidation at which the carbon and hydrogen of formaldehyde are incorporated into the methyl groups of choline and creatine has been reinvestigated. Furthermore, the methyl group of methionine was also of interest in this regard, and it was also considered important to examine the level of oxidation of the formaldehyde carbon that occurred before incorporation into the hydroxymethyl group of serine. Since the urinary formate might have a bearing on the metabolism of formaldehyde, this substance was also isolated and examined for its isotopic content.