Abstract
Monogalactosyldiacylglycerol (MGDG) is a major lipid in oxygen-evolving photosynthetic organisms and constitutes up to 50% of plastid lipids. Although the lipid composition of photosynthetic membranes is very similar between plant chloroplasts and cyanobacteria, their biosynthetic pathways of MGDG are thought to be different. MGDG synthase (MGD) and monoglucosyldiacylglycerol synthase (MGlcD) are involved in MGDG synthesis in plants and in cyanobacteria, respectively.
Recently we found that the green alga Chlamydomonas reinhardtii carries both genes for MGD and MGlcD. In this study, we cloned MGDG synthase gene of C. reinhardtii (CrMGD) and analyzed enzymatic properties of this recombinant enzyme, comparing with that of Cucumis sativus MGD (CsMGD). The optimal pH for CrMGD activity is pH7.5 and CrMGD was activated when magnesium ions or calcium ions were added to the reaction mixture. Similar results were also observed for CsMGD. However CsMGD activity was increased by addition of PA after solubilization with LDAO, whereas CrMGD did not show significant activation, suggesting that the regulation of MGDG synthesis in C. reinhardtii might be different from that in higher plants.
