Neutral glycolipids and gangliosides of umbilical cord and adult human erythrocytes were separated by high performance liquid chromatography, and each fraction was analyzed by direct binding of anti-I (Ma) and anti-i (Den) on solid phase glycolipid-lecithin-cholesterol. The I- and i-active glycolipids were isolated and their structures were determined by methylation analysis and direct probe mass spectrometry. The major I antigen in adult erythrocytes, showing a remarkable binding activity with anti-I(Ma), was found in one neutral glycolipid fraction, designated fraction y4, which was identified as a mixture of two glycolipids of a new type, lactoisooctaosylceramide and monofucosyllactoisooctaosylceramide (for structures, see Table I). In addition, two gangliosides displaying direct binding activity with anti-I(Ma) were identified as monosialoganglioside G8, as previously described and disialosyllactoisooctaosylceramide, which showed the same level of I activity as the y4 glycolipid. The same ganglioside was recently isolated and characterized by Kundu and co-workers. The major i-active glycolipid antigen in umbilical cord erythrocytes, showing a strong binding activity with anti-i(Den), was a neutral glycolipid, x4a, which was identified as lactonorhexaosylceramide. This glycolipid without fucosyl or sialosyl substitution has not been isolated previously and was present as an obvious normal component of umbilical cord erythrocytes, but an extremely minor component of adult erythrocytes. Sialosyllactonorhexaosylceramide (G6) was isolated and characterized as a second i antigen of umbilical cord erythrocytes, but showed a very weak binding activity with the anti-i antibody. Although these sialosyl derivatives displayed only weak activity, the chemical quantity of the sialosyl derivatives is significantly large in fetal erythrocytes; therefore, Ii activity of human erythrocytes, in general, must be significantly dependent on sialosyl derivatives in addition to unsubstituted structures.

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