Structure of the Human Erythrocyte Blood Group P₁ Glycosphingolipid

A glycosphingolipid with blood group P₁ activity was extracted from an acetone powder of human erythrocyte stroma with chloroform-methanol. It was purified by chromatography on columns of silicic acid and by preparative thin-layer chromatography of the fully acetylated and deacetylated glycolipid. The purified glycolipid contained galactose, N-acetylglucosamine, and glucose in a molar ratio of 3:1:1. Treatment of the P₁ glycolipid with fig α-galactosidase released a single galactosyl residue and destroyed the blood group activity, and the α-galactosidase product had the same chromatographic mobility as paragloboside. Substitution sites on the neutral sugars of the P₁ glycolipid and the α-galactosidase product were established by identification of methylated alditol acetates, and substitution on N-acetylglucosamine was determined by identification of methyl glycoside derivatives. The terminal nonreducing disaccharide of the P₁ glycolipid is Gal(α,1→4)Gal. N-Acetylglucosamine was identified as the next sugar in sequence by mass spectrometric analysis of the permethylated P₁ glycolipid. On the assumption that the glucose residue is linked to ceramide, we propose the following structure for the P₁ glycolipid: Gal(α,1→4)Gal(β,1→4)Glc-NAc(β,1→3)Gal(β,1→4)Glc-Cer.