On the Accessibility and Localisation of Cerebrosides in Central Nervous System Myelin
Cerebrosides are concentrated in the myelin sheath where they account for about 20% of the total lipid of the membrane. The present paper is concerned with the role and localisation of these glycolipids in the myelin lamellae. Isolated central nerve myelin preparations have been treated with two probes to investigate cerebroside accessibility in the membrane. The action of galactose oxidase on the galactose headgroups of cerebrosides is followed and quantitated by recovery of the modified glycolipid and resolution of either the 6-aldehydo sugar or galactose remaining by gasliquid chromatography. With isolated myelin preparations only some 40–50% of the cerebroside galactose is attacked by galactose oxidase at 20°C. With periodate at 20°C over 90% of the galactose headgroups are oxidised in 3 h while the figure is 50–55% over the same time period at 4°C rising to 85% after 22 h. With multilamellar liposomes of mixed myelin lipids only some 20–25% of the available cerebroside is oxidised at 4°C, the reaction being complete in 2 h. The results are discussed in relation to the disposition of cerebroside in the myelin lamellae. A major location on the external face of the membrane system (intraperiod dense line) is favoured. A role for cerebroside in myelin in terms of increasing the stability and resistance of the lipid phase to ion movement is suggested.
KeywordsMyelin Sheath Lipid Phase Sodium Periodate Galactose Oxidase Multilamellar Liposome
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- 5.Gregson, N.A., Personal communication (1977).Google Scholar
- 6.Hubbard, A.L. and Cohn, Z.A., Specific labels for cell surfaces, in Biochemical Analysis of Membranes ( A.H. Maddy, ed.) Chapman & Hall, London (1976) pp. 427–501.Google Scholar
- 7.Ladbrooke, B.D., Jenkinson, T.J., Kamat, V.B. and Chapman, D., Physical studies of myelin, Biochim. Biophys. Acta 164 (1968) 101–109.Google Scholar
- 8.Linington, C. and Rumsby, M.G., Localisation of cerebroside in central nervous system myelin lamellae: An initial approach, Biochem. Soc. Trans. 5 (1977) 196-198.Google Scholar
- 10.Oldfield, E. and Chapman, D., Molecular dynamics of cerebroside-cholesterol and sphingomyelin-cholesterol interactions: Implications for myelin membrane structure. FEBS Letts. 21 (1972) 303-306.Google Scholar
- 11.Pascher, I., Molecular arrangements in sphingolipids: Conformation and hydrogen bonding of ceramide and their implication in membrane stability and permeability, Biochim. Biophys. Acta 455 (1976) 431–451.Google Scholar
- 12.Poduslo, J.F., Distribution of galactose residues in surface membrane glycoproteins and glycolipids of the intact myelin sheath, Abstract No. 319, Fifth ISN Conference, Barcelona (1975).Google Scholar
- 13.Poduslo, J.F., Quarles, R.H. and Brady, R.O., External labelling of galactose in surface membrane glycoproteins of the intact myelin sheath, J. Biol. Chem.251 (1976) 153-158.Google Scholar
- 14.Rumsby, M.G. and Crang, A.J., The myelin sheath - a structural examination, Cell Surface Reviews 4 (1977) in press.Google Scholar
- 15.Rumsby, M.G., Riekkinen, P.J. and Arstila, A.V., A critical evaluation of myelin purification: Non-specific esterase activity associated with central nerve myelin preparations, Brain Res. 24 (1970) 495-516.Google Scholar
- 16.Sackett, D., Estimation of cholesterol, J. Biol. Chem. 64 (1925) 203.Google Scholar