GANGLIOSIDE COMPOSITION AND CONTENT OF RAT‐BRAIN SUBCELLULAR FRACTIONS

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Abstract
Abstract—The composition and content of gangliosides from rat‐brain microsomal, synaptosomal, mitochondrial and myelin fractions were studied. Outer membranes of synaptosomes were also isolated, separated into subfractions and investigated. Of all the fractions studied the outer membranes of synaptosomes are richest in gangliosides, in one of their sub‐fractions the concentration of gangliosides per mg of protein is five times higher than in the homogenate. Microsomes are rich in gangliosides as well, but to a lesser degree, whereas the mitochondrial fraction contains considerably smaller amounts of gangliosides per mg of protein than does the homogenate. The ganglioside pattern of outer membranes of synaptosomes and of their subfractions is somewhat different from that of the homogenate; the outer membranes contain approximately one‐third less monosialogangliosides. On the contrary a very high content of monosialogangliosides is characteristic of the ganglioside pattern of the myelin fraction. In this fraction monosialoganglioside GMI(nomenclature of Svennerholm, 1963) constitutes 60–63 per cent of ganglioside sialic acid, or 75–80 molar per cent of gangliosides, the content of di‐ and trisialogangliosides being much lower than in other fractions. Fatty acid and long chain base composition of gangliosides from synaptosomal and microsomal fractions and homogenate is very similar, almost identical. In gangliosides from myelin fractions the relaitve content of palmitic and monoenoic acids is higher and that of arachinic acid and C20‐sphingosine—lower than in other fractions studied. The difference in ganglioside composition of synaptosomes and their outer membranes and on the other hand of myelin appears to reflect the difference in ganglioside composition of neuronal and oligodendroglial plasma membranes.