Purification and Characterization of UDP-GAL: Ceramide Galactosyltransferase and Reconstitution of its Activity by Incorporation into Liposomes

Abstract

The UDP-gal: ceramide galactosyltransferase (CGalT) (EC 2.4.1.45) catalyzes the last step in the synthesis of the myelin- characteristic lipid, galactosylceramide (Morell and Radin, 1969). The Oligodendroglia and Schwann cells are the primary site of localization of this enzyme, and its presence in myelin has been firmly established biochemically and (Neskovic et al., 1973; Costantino-Ceccarini and Suzuki, 1975; Koul and Jungalwala, 1981; Roussel et al., 198ssel et al., 1987). While considerable amounts of information are available regarding the properties of the enzyme in the literature, the majority of these studies were carried out with membrane-bound enzyme preparations, and to date, nothing is known about in vivo regulation of the activity of this enzyme during development. The question of regulation of the synthesis of galactosylceramide and other myelin lipids must be considered in a wider context of regulation of synthesis of the myelin membrane. Considerable progress has been made in the understanding of synthesis of myelin-specific proteins at the molecular level. Similar studies with respect to the myelin-specific lipids have been hampered by the difficulties encountered in the purification of the respective synthetic enzymes due to the highly hydrophobic nature of these proteins.