Human glucocerebrosidase catalyses transglucosylation between glucocerebroside and retinol.
The basal activity of human placental glucocerebrosidase is elevated 16-fold by n-pentanol when assayed using p-nitrophenyl beta-D-glucopyranoside (pNPGlc) as the beta-glucosidase substrate. This enhancement of activity is the result of the formation of a transglucosylation product, n-pentyl beta-D-glucoside, in rate-determining competition with the hydrolytic reaction. The transglucosylation product accounts for approximately 80% of the reaction product generated in the presence of n-pentanol (0.18 M) when either glucocerebroside or pNPGlc was used as the substrate. This stimulatory effect can be increased an additional 3-fold by the inclusion of phosphatidylserine (20 micrograms/ml) or sodium taurodeoxycholate (0.3%, w/v) in the incubation medium. In the presence of retinol, glucocerebrosidase also catalyses the synthesis of a novel lipid glucoside, retinyl glucoside, when either glucocerebroside or pNPGlc serves as the substrate. The reaction product was identified as retinyl beta-D-glucoside, based on its susceptibility to hydrolysis by almond beta-D-glucosidase and the subsequent release of equimolar amounts of retinol and glucose. The rate of retinyl-beta-glucoside formation is dependent on the concentration of retinol in the incubation medium, reaching saturation at approximately 0.3 mM retinol. Retinyl beta-D-glucoside is a substrate for two broad-specificity mammalian beta-glucosidases, namely the cytosolic and membrane-associated beta-glucosidases of guinea pig liver. However, retinyl beta-D-glucoside is not hydrolysed by placental glucocerebrosidase. These data indicate that the glucocerebrosidase-catalysed transfer of glucose from glucocerebroside to natural endogenous lipid alcohols, followed by the action of a broad-specificity beta-glucosidase on the transglucosylation product, could provide mammals with an alternative pathway for the breakdown of glucocerebroside to glucose and ceramide.
Vanderjagt
D J
DJ
Department of Biochemistry, University of New Mexico School of Medicine, Albuquerque 87131.
Fry
D E
DE
Glew
R H
RH
D000818:Animals; D002384:Catalysis; D004789:Enzyme Activation; D005960:Glucosides / Q000378:metabolism; D005962:Glucosylceramidase / Q000378:metabolism*; D005963:Glucosylceramides / Q000378:metabolism*; D006031:Glycosylation; D006168:Guinea Pigs; D006801:Humans; D006868:Hydrolysis; D000439:Pentanols / Q000378:metabolism; D014801:Vitamin A / Q000378:metabolism*
D005960:Glucosides; D005963:Glucosylceramides; D000439:Pentanols; D014801:Vitamin A; C025193:4-nitrophenyl beta-D-glucoside; D005962:Glucosylceramidase; C024999:n-pentanol