The enzyme converts monogalactosyldiacylglycerol to digalactosyldiacylglycerol, trigalactosyldiacylglycerol and tetragalactosyldiacylglycerol. All residues are connected by beta linkages. The activity is localized to chloroplast envelope membranes, but it does not contribute to net galactolipid synthesis in plants, which is performed by EC 188.8.131.52, monogalactosyldiacylglycerol synthase, and EC 184.108.40.206, digalactosyldiacylglycerol synthase. Note that the beta,beta-digalactosyldiacylglycerol formed by this enzyme is different from the more common alpha,beta-digalactosyldiacylglycerol formed by EC 220.127.116.11. The enzyme provides an important mechanism for the stabilization of the chloroplast membranes during freezing and drought stress.
EC 18.104.22.168 created 1990, modified 2005, modified 2015