Further characterization of equine brain gangliosides: the presence of GM3 having N-glycolyl neuraminic acid in the central nervous system.

Equine brain gangliosides were isolated and their structures were characterized, to examine whether equine brain has N-glycolyl neuraminic acid in gangliosides, since other mammals predominantly possess N-acetyl neuraminic acid in brain gangliosides, and equine erythrocytes and organs except the brain have gangliosides exclusively containing N-glycolyl neuraminic acid. The gangliosides purified from the brain were identified by proton NMR spectroscopy and mass spectrometry, as well as GLC, resulting in their identification as GM4, GM3, GM2, GM1, GD1a, GD1b, and GT1b. Of these gangliosides, GM3 possessed N-glycolyl neuraminic acid as a minor component (18% of the total GM3), whereas other gangliosides exclusively contained N-acetyl neuraminic acid. The N-glycolyl neuraminic acid residue of the GM3 was confirmed by TLC immunostaining. The possibility of contamination of the GM3 by erythrocytes was eliminated based on the finding that the lipid compositions were characteristic of brain gangliosides. The presence, even as a minor component, of the N-glycolyl neuraminic acid in equine brain gangliosides is exceptional among the sialic acid species in mammalian central nervous system.