Sphingolipid base metabolism. Stereospecific uptake of proton in the enzymatic conversion of sphinganine 1-phosphate to ethanolamine 1-phosphate.

D-erythro-(2S, 3R)-Sphinganine 1-phosphate was incubated with rat liver microsomes in the presence of tritiated water. [3H]Ethanolamine 1-phosphate was isolated and converted, through a combination of enzymatic and chemical reactions, to [3H]glycine. The labeled glycine was incubated with D-amino acid oxidase, an enzyme which, in the catalysis of the conversion of glycine to glyoxylic acid, specifically removes the hydrogen in the S configuration at carbon atom 2 of glycine. Essentially complete retention of the labeled hydrogen occurred upon conversion to glyoxylic acid. The combined results indicate that the conversion of D-erythro-(2S,3R)-sphinganine 1-phosphate to palmitaldehyde and ethanolamine 1-phosphate, catalyzed by sphinganine-1-phosphate lyase of rat liver microsomes, proceeds with the stereospecific incorporation of 1 atom of solvent hydrogen into the R configuration of ethanolamine 1-phosphate.