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 2.4.1.46, monogalactosyldiacylglycerol synthase, and EC 2.4.1.241, digalactosyldiacylglycerol synthase. Note that the beta,beta-digalactosyldiacylglycerol formed by this enzyme is different from the more common alpha,beta-digalactosyldiacylglycerol formed by EC 2.4.1.241. The enzyme provides an important mechanism for the stabilization of the chloroplast membranes during freezing and drought stress.
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REACTION
REACTION DIAGRAM
COMMENTARY
ORGANISM
UNIPROT
LITERATURE
2 a 1,2-diacyl-3-O-(beta-D-galactosyl)-sn-glycerol = a 1,2-diacyl-3-O-[beta-D-galactosyl-(1->6)-beta-D-galactosyl]-sn-glycerol + a 1,2-diacyl-sn-glycerol
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 2.4.1.46, monogalactosyldiacylglycerol synthase, and EC 2.4.1.241, digalactosyldiacylglycerol synthase. Note that the beta,beta-digalactosyldiacylglycerol formed by this enzyme is different from the more common alpha,beta-digalactosyldiacylglycerol formed by EC 2.4.1.241. The enzyme provides an important mechanism for the stabilization of the chloroplast membranes during freezing and drought stress.
by further transfer of galactosyl residues to the digalactosyldiacylglycerol, trigalactosyldiacylglycerol and tetragalactosyldiacylglycerol are also formed
by further transfer of galactosyl residues to the digalactosyldiacylglycerol, trigalactosyldiacylglycerol and tetragalactosyldiacylglycerol are also formed
by further transfer of galactosyl residues to the digalactosyldiacylglycerol, trigalactosyldiacylglycerol and tetragalactosyldiacylglycerol are also formed
alpha-linolenic acid causes drastic increase in activity under limiting concentrations of MgCl2, without affecting its maximum activity at higher MgCl2 concentration, free alpha-linolenic acid alone does not affect the activity
in the lipid extract form cells expressing chlo02003782 monogalactosyldiacylglycerol is detected, therefor, this open reading frame is assigned as a beta-galactosyltransferase
under normal growth conditions, the in vivo activity of the galactolipid:galactolipid galactosyltransferase is not detectable in the wild type, but becomes apparent in the tgd mutant. The enzyme does not provide the bulk of glactoglycerolipids in the chloroplast, but is speculated to play a role during ozone-induced injury or possibly during senescence of leaves when chloroplast membranes are turned over
dgd2 null mutant, no effects on growth and lipid composition. Dgd1 dgd2 double null mutant, only trace amounts of digalactosyldiacylglycerol, but some monogalactosyldiacylglycerol and unusual oligogalactolipids like tri- and tetragalactosyldiacylglycerol
analysis of dgd1 and dgd2 double mutants show that galactolipid:galactolipid galactosyltransferase is different from the genuine digalactosyldiacylglycerol synthases DGD1 and DGD2, because chloroplasts of a double mutant still are capable of oligogalactolipid biosynthesis.
Disruption of the two digalactosyldiacylglycerol synthase genes DGD1 and DGD2 in Arabidopsis reveals the existence of an additional enzyme of galactolipid synthesis
2.4.1.184 galactolipid galactosyltransferase
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