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A new ganglioside, containing an alkali-labile linkage, was extracted from mouse brain and purified.It represents 5.2% of total lipid-bound sialic acid in the tissue and was obtained in pure form with a yield of about 50%.It contains sphingosine, glucose, galactose, N-acetylgalactosamine, and sialic acid in the molar ratio 1/1/2/1/3 and, upon exhaustive neuraminidase treatment, gives the monosialoganglioside GMl.Partial acid hydrolysis, methylation analysis, gas-liquid chromatography-mass spectrometry, and chromium trioxide oxidation studies showed its basic neutral glycosphingolipid core to be ganglio-N-tetraose ceramide, Gall 3GalNAcl + 4 G d l -+ 4Glcl + 1'ceramide.T w o of the three sialic acid residues are Nacetylneuraminic acid and one, as shown by gas-liquid chromatography-mass spectrometry (GLC-MS), is 9-0- acetyl-N-acetylneuraminic acid, which contains the alkali-labile linkage.9-0-Acetyl-N-acetylneuraminic acid is a-ketosidically linked to position 8 of the N-acetylneuraminic acid residue bound to position 3 of the internal galactose.The third N-acetylneuraminic acid residue is linked to position 3 of the external galactose.The complete structure of the studied ganglioside is as follows: NeuAca2 * 3 G a l B l j 3GalNAcBl+ 4(9-0-Ac-NeuAca2 --* bNeuAca2 4 3)Gal/31+ 4GlcBl--., 1'-Nacylsphingosine, and it can be considered as a derivative of the trisialoganglioside G;Tlb.
Ghidoni et al. (Tue,) studied this question.