ABSTRACT
Galactolipids and sulfolipids are characteristic plant membrane glycerolipids. Galactolipids are neutral amphipatic lipids. Together, galactolipids and sulfoquino-vosyldiacylglycerol (SQDG) comprise four fifths of spinach lamellar lipoprotein. Of these lipids, 90% are monogalactosyl-diacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), whereas SQDG makes up the rest. Plant SQDG has a high proportion of saturated fatty acids, much more than galactolipids. The differences among galactolipid molecules are mostly confined to the diacylglycerol portion. The same is true for SQDG. At least two major diacylglycerol structures are found in plastid glycerolipids. Heinz recently demonstrated that chemically synthesized UDP-sulfoquinovose can be used by isolated envelope membranes for SQDG synthesis, thus demonstrating that the SQDG biosynthetic pathway proposed by Shibuya could have some physiological significance. This chapter considers the final steps in galactolipid biosynthesis, that is, the biochemical characterization of MGDG synthase and its purification, and the possible pathway for DGDG synthesis.
