GANGLIOSIDES OF HUMAN MYELIN: SIALOSYLGALACTOSYLCERAMIDE (G₇) AS A MAJOR COMPONENT

Abstract— Gangliosides were isolated from purified human myelin in a yield of 62 μg of lipid‐bound sialic acid per 100 mg of dry myelin. Sialosylgalactosyl ceramide (G₇) was found to be a major component of the ganglioside fraction, amounting to 15 per cent of the total sialic acid. It accounted for 10 per cent of lipid‐bound sialic acid in adult human white matter, making it the third most abundant ganglioside on a molar basis. These results were obtained with an improved method for isolating total gangliosides in high yield, by employing DEAE‐Sephadex column chromatography. Myelin from other mammalian species had considerably less G₇, and there were also indications of maturational changes. Both 2‐hydroxy and unsubstituted fatty acids were components of the ceramide unit, in a ratio of 3:2, respectively. The overall fatty acid pattern was very similar to that for myelin cerebroside and sulphatide. Long‐chain bases included only C₁₈ species, with sphingosine predominating (>90 per cent). These observations suggest a metabolic relationship between G₇ and either cerebroside or sulphatide.