Ceramide glucosyltransferase

Ceramide glucosyltransferase, EC2.4.1.80, is a glycosyltransferase that transfers a glucose-derived group from UDP-glucose to a ceramide acceptor, producing glucosylceramide and uridine diphosphate. The accepted reference reaction specifically names an N-acylsphingosine acceptor and a D-glucosyl-N-acylsphingosine product.^[ref]

The transfer changes the lipid headgroup while retaining the ceramide portion. The reaction therefore differs from simply mixing free glucose with a lipid, and from transferring an intact nucleotide onto the lipid. The uridine diphosphate moiety leaves while the glucose-derived residue remains attached through a glycosidic bond.

For a stoichiometric example, suppose a defined mixture begins with12nanomoles of UDP-glucose and5nanomoles of the accepted ceramide, with no replenishment or side reactions. One glucose-transfer event consumes one donor and one acceptor, so product formation is bounded above by5nanomoles, even though donor remains. This upper bound does not assert complete conversion or determine a reaction rate.

A conceptual activity assay must identify the glucosylated lipid and compare an appropriate enzyme-free control: disappearance of donor alone could reflect another reaction. The IUBMB record also lists other possible acceptors and donors, reminding us that an accepted reference reaction is not a claim of absolute specificity for every preparation.^[ref]