Structure and genetic polymorphism of blood group A-active glycosphingolipids of the rat large intestine.

ABSTRACT

Study of blood group A- and B-active glycosphingolipid content of the epithelium of the large intestine of 16 strains of inbred rats led to the discovery of two related strains, SHR and WKY, devoid of A-active glycolipids, whereas all strains expressed B-active glycolipids. This finding evidenced a new A/non-A genetic polymorphism in the rat. Blood group A-active glycolipids were isolated from the large intestine of F344 rats and purified by affinity chromatography on immobilized Helix pomatia lectin. Three glycolipid fractions were separated by preparative thin-layer chromatography and characterized by electron-impact mass spectrometry of their permethylated and permethylated-LiAlH4-reduced derivatives. They were identified as a tetraglycosylceramide (A-4), a hexaglycosylceramide (A-6), and a difucosylated heptaglycosylceramide (A-7) with small amounts of monofucosylated octaglycosylceramide (A-8). Methylation analysis and fragmentation indicated that A6 and A-8 had a lacto- and A-7 a neolactotetraosylceramide core, respectively, identical to the core structures of B-6 and B-7 previously characterized in the large intestine of WF rats (Angström et al. (1987) Biochim. Biophys. Acta 926, 79-86). Upon methylation analysis, B-6 and B-7 purified from SHR (A-deficient) and F344 (A-expressing) were found identical to those of WF rats. This result indicated that precursor substrates for the synthesis of A-active glycolipids were available in SHR rats and thus the genetic deficiency of A-active glycolipid expression probably originated in a defect of the termination of the blood group A determinant by the alpha-3-N-acetylgalactosaminyltransferase.