In enzymology, a galactolipid galactosyltransferase is an enzyme that catalyzes the chemical reaction 2 3--1,2-diacyl-sn-glycerol ⇌ {\displaystyle \rightleftharpoons } 3-[alpha-D-galactosyl--beta-D-galactosyl]-1,2-diacyl-sn- glycerol + 1,2-diacyl-sn-glycerolHence, this enzyme has one substrate, 3--1,2-diacyl-sn-glycerol, but 3 products: [[3-[alpha-D-galactosyl--beta-D-galactosyl]-1,2-diacyl-sn-]], glycerol, and 1,2-diacyl-sn-glycerol. Wikipedia