Structures of ceramide tetrasaccharides from various sources: uniqueness of rat kidney ceramide tetrasaccharide

Methylation analysis of ceramide tetrasaccharide isolated from human erythrocytes gave acetates of 2,3,6-tri-O-methylgalactitol and 2,4,6-tri-O-methylgalactitol in a ratio of 1:1, and about 50% of the galactose was oxidized by periodate. Rat kidney ceramide tetrasaccharide gave, in contrast, a much larger proportion of the acetates of 2,4,6-tri-O-methylgalactitol (ratio 1:0.3), and less than 20% of the galactose was oxidized by periodate. Sequential degradation by beta-N-acetylhexosaminidase, alpha-galactosidase, and beta-galactosidase showed ceramide tetrasaccharides to have identical carbohydrate sequences and anomeric structures. The major part of ceramide trihexoside derived from rat kidney ceramide tetrasaccharide migrated on thin-layer chromatography more slowly than that derived from other ceramide tetrasaccharides. The structure of a major part of rat kidney ceramide tetrasaccharide was thus determined to be GalNAcbeta(1-->3)Galalpha(1-->3)Galbeta(1-->4)Glcbeta(1-->1)Cer, whereas other ceramide tetrasaccharides have Galalpha(1-->4) structure at the penultimate residue.