In enzymology, a galactosyldiacylglycerol alpha-2,3-sialyltransferase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are CMP-N-acetylneuraminate and 1,2-diacyl-3-beta-D-galactosyl-sn-glycerol, whereas its 3 products are CMP, 1,2-diacyl-3-[3-(alpha-D-N-acetylneuraminyl)-beta-D-galactosyl]-sn-, and glycerol.
This enzyme belongs to the family of transferases, specifically those glycosyltransferases that do not transfer hexosyl or pentosyl groups. The systematic name of this enzyme class is CMP-N-acetylneuraminate:1,2-diacyl-3-beta-D-galactosyl-sn-glycerol N-acetylneuraminyltransferase. This enzyme participates in glycerolipid metabolism.