Structural characterization of the acidic phosphonoglycosphingolipids in nervous system of Aplysia kurodai and studies on their neurobiological function.

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We isolated four phosphonoglycosphingolipids, designated as FGL-IIA, FGL-IIb, FGL-V and F-21, from the nervous system of A. kurodai by Iatrobeads column chromatography using three solvent systems and elucidated their complete structures, respectively.Pyruvic acid attached as a ketal to 0-3 and 0-4 of the terminal galactose of the oligosaccharide chain in FGL-IIa, FGL-IIb and FGL-V.We raised a polyclonal antibody against FGL-IIb and examined the antigens that reacted with this anti-FGL-IIb antiserum by enzyme immunostaining on TLC plates. The antiserum reacted with FGL-IIb, FGL-I, FGL-IIa, FGL-V and F-9, which were identified in ganglia and nerve fibers on TLC plates. Esterification or reduction of the pyruvic acid moiety of FGL-IIb resulted in loss of its antigenicity against the antiserum, and saponification of the acid methanol-treated FGL-IIb restored the reactivity. These results indicate that the epitope for the anti-FGL-IIb antibodies includes the free carboxyl group of pyruvic acid in FGL-IIb.We also examined the localization of antigens in the tissues of A. kurodai immunohistochemically. With this antiserum, only nerve bundles were stained distinctly. From histochemical findings in cryostat sections pretreated with chloroform:methanol (2:1, v/v) and from results by Western blot analysis of the nervous system, the staining was concluded to be due to glycolipid antigens. These acidic phosphonoglycosphingolipids containing pyruvic acid may be involved as ligand in neurite outgrowth and cell adhesion.