PHYLOGENETIC, DEVELOPMENTAL AND BIOCHEMICAL STUDIES OF MYELIN GANGLIOSIDES
COCHRAN, FREDERICK BICE, JR.
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Myelin was isolated from the brains of eighteen species and spinal cords of two. Mature animals were used. Myelin purity was assessed by measuring protein, phospholipid and 2',3'-cyclic nucleotide 3'-phosphohydrolase and by characterizing the proteins by SDS-PAGE. Gangliosides were isolated from all myelin samples and from whole brain, gray and white matter of several species. Total concentrations ranged from a low of 25 (mu)g of lipid-bound sialic acid per 100 mg of myelin for goldfish to a high of 395 for turkey brain myelin. Ganglioside patterns were determined by densitometric scanning of the thin-layer plates. Primates and higher vertebrates generally had more ganglioside and a predominance of monosialogangliosides in their myelin, while lower vertebrates had less ganglioside and a predominance of polysialogangliosides. Mammals had variable amounts of G(,M4); the highest concentration was found in Rhesus monkey myelin (25.3 per cent of lipid-bound sialic acid). Other mammals had less while G(,M4) was not detectable in frog, fish and alligator myelin. Chicken, pigeon and turkey myelin proved exceptional, having the largest amounts of G(,M4) (24 - 32%) and total ganglioside (251 - 395 (mu)g of lipid-bound sialic acid per 100 mg. of myelin).;To observe developmental changes in avian species, myelin was isolated from the brains of chickens aged 17 days embryonic through 18 months post-hatching. Gangliosides were isolated and the myelin proteins characterized. The concentration of total and individual gangliosides and proteins remained constant throughout development, in contrast to mammalian species. G(,M1) and G(,M4) were present in the same concentration in embryonic and adult chicken myelin.;A sialosyltransferase responsible for the biosynthesis of G(,M4) was characterized and compared to one responsible for the biosynthesis of G(,M3). Evidence is presented for: (1) the existence of an oligomeric sialosyltransferase responsible for G(,M3) synthesis, and (2) a separate sialosyltransferase activity responsible for the biosynthesis of G(,M4).