Occurrence of 2-O-acyl galactosyl ceramide in human and bovine brains

Ester cerebrosides isolated from whale brain were demonstrated to be a mixture of 6-O-acyl, 2-O-acyl, 4-O-acyl, and 3-O-acyl galactosyl ceramides in that order of content (Yasugi, E., et al. (1982) J. Biochem. 91, 1121-1127). However, the existence of 2-O-acyl and 4-O-acyl galactosyl ceramides has not been reported for other mammalian brains. In the present work, ester cerebrosides isolated from bovine and human brains were examined in order to determine whether the above-mentioned substitution is only present in whale brain or also present in other mammalian brains. For determining the substituted positions of the acyl group on the galactose moiety, free hydroxyl groups of ester cerebrosides were protected with dihydropyran, deacylated by mild alkali treatment, and then subjected to permethylation. Finally, the methylated galactitol acetates obtained by hydrolysis and reduction were analyzed by gas chromatography and gas chromatography/mass spectrometry. By these procedures, ester cerebrosides obtained from bovine and human brains were demonstrated to be not only 6-O-acyl and 3-O-acyl galactosyl ceramides but also 2-O-acyl and 4-O-acyl galactosyl ceramides similar to those of whale brain.