Specificity and Developmental Changes of an Endogenous Inhibitor of Ceramide Galactosyltransferase
Galactocerebrosides are characteristic components of the myelin sheeth of both central and peripheral nervous system. Two possible pathways have been proposed for their biosynthesis: one through psychosine which is synthesized from sphingosine and UDP galactose, Psychosine, in turn, may be acylated to form galactocerebrosides (Brady 1962). The other pathway involves the transfer of galactose to ceramide by the UDP galactose: ceramide galacto-syltransferase. At the present time the main biosynthetic pathway for the synthesis of galactosylceramide appears to be the second pathway (Morell and Radin, 1969; Basu et al., 1971). The galactosyltransferase that catalyzes such reaction has been studied only in the membrane bound form. Claim of a soluble and partially purified preparation has been reported (Neskovic et al., 1976) and more recently an improved preparation has been described by the same authors (Neskovic et al., 1986). Developmental studies have shown an increase in the enzyme activity concomitant to the maximum myelin accumulation followed by a sharp drop (Costantino-Ceccarini et al., 1972). Subcellular fractionation has shown that the enzyme is primarily but not exclusively localized in the microsomal fraction of the brain (40–45%). Later studies have shown that the enzyme is also localized in myelin and axolemma enriched fractions (Costantino-Ceccarini and Suzuki, 1975 and Costantino-Ceccarini et al., 1979).
KeywordsDevelopmental Change Microsomal Fraction Endogenous Inhibitor Brain Microsome Myelin Fraction
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