Effect of hydrogenation of glucosyl- and galactosylceramide on their enzymatic hydrolysis.

Our earlier observation that N-stearoyl- and N-lignoceroyl-glucosyl-dihydro-sphingosines have much lower affinity to the hydrolytic enzyme, glucosylceramidase, than the natural mixture of glucosylceramide [11] has been further pursued with catalytically hydrogenated natural substrate. Similar experiments were also carried out for hydrolysis of galactosylceramide of different structures by galactosylceramidase. The hydrogenation procedure completely saturated both fatty acid and long chain base moieties. For either enzyme, the hydrogenated natural substrate had affinity approximately half of the untreated natural substrate mixture. However, the synthetic glucosylceramides which contained a single saturated fatty acid and dihydrosphingosine had generally still lower affinity than the hydrogenated natural mixture. When two synthetic substrates of different fatty acids were mixed together, the affinity to the enzyme increased to a level much higher than that of either of the synthetic substrates alone and reached that of the hydrogenated natural substrate mixture. The findings were similar for galactosylceramide hydrolysis except that the synthetic substrate with palmitic of stearic acid had affinity to the enzyme not much lower than that of the hydrogenated natural substrate mixture. These effects of different structures on their enzymatic hydrolysis remained similar when other constituents of the assay mixture, such as the buffer and detergents, were varied.