Isolation of an Endogenous Inhibitor of Ceramide Glycosyltransferases from Rat Brain
Galactosylceramide is generally considered to be the characteristic constituent of myelin, although recent studies have shown that this lipid is also present in a substantial concentration in myelinated axons freed of myelin (1,2). Reflecting their primary localization in myelin, galactosylceramide biosynthesis shows a peak of activity in developing brain, concomitant with the period of maximal myelin accumulation (3,4). The terminal enzymatic step in the biosynthetic pathway of galactosylceramide is galactosylation of α-hydroxy fatty acid-containing ceramide (HFA-ceramide), catalyzed by UDP-galactose:ceramide galactosyltransferase (E.C. 2.4.1. 62)(5). This enzyme is primarily localized in the microsomal fraction by the conventional subcellular fractionation procedure. However, small proportions of this enzyme are also present in the myelin sheath (6,7) and in an axolemma-enriched fraction (8). The specific activity of the galactosyltransferase in the axolemma fraction is similar to that in the microsomal fraction (8).
KeywordsMicrosomal Fraction Endogenous Inhibitor Microsomal Protein Enzyme Source Inhibitor Preparation
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