On the biosynthesis of cerebrosides containing 2-hydroxy acids. Mass spectrometric evidence for biosynthesis via the ceramide pathway.

The conversion of deuterium-labeled ceramide to cerebroside has been studied. A mixture of N-(2’+hydroxy [4’,4’,5’,5’-2H4]hexadecanoyl) D-eryfhYO-1,3-dihydroxy-2amino-4-frans-[4,5-*H2]octadecene and N-(2’-D-hydroxy hexadecanoyl) D-eryfhro-l,3-dihydroxy-2-amino-4-frans-[33Hl]octadecene was incubated with mouse brain microsomes and a UDP-galactose regenerating system. Both galactosyl ceramide and glucosyl ceramide were formed. The ceramide monohexosides were analyzed by gas-liquid chromatographymass spectrometry as the trimethylsilyl ether derivatives both as intact molecules and after degradation to ceramides. The analysis conclusively showed that both compounds had been synthesized via the ceramide pathway. A third product from the incubations was identified as free sphingosine.