Studies on the conversion in vitro of serine to ethanolamine by rat liver and brain.

After the original demonstration by Stetten (1) that the nitrogen atom of DL-serine-N15 is converted to the nitrogen of ethanolamine in the intact rat, considerable evidence has accrued to indicate that in mammalian tissues L-serine is decarbosylated to ethanolamine. Not only are the B-carbon, B-hydrogen, and nitrogen of serine extensively utilized as a unit for the synthesis of the ethanolamine moiety of choline, but, in addition, glycine and formate are converted to serine before incorporation into ethanolamine (2-4). Furthermore, D-serine (5) and the carbon 1 of glycine (5, 6) are not precursors of ethanolamine in the rat. However, despite the demonstration of ethanolamine synthesis from serine in the intact animal, little is known about the mechanism of this conversion. The conversion of serine-Cl4 to ethanolamine has been studied in rat liver and brain slices and in rat liver homogenates. This communication presents evidence that in these tissues a serine metabolite, either phosphatidylserine or a precursor of phosphatidylserine, is converted to ethanolamine.