The path of carbon in photosynthesis of the lipids

Abstract

The rates of C 11 incorporation into lipids and their components during steady-state photosynthesis in C 11O 2 by Chlorella pyrenoidosa reveal the metabolic importance of the galaclolipids and phosphatidyl glycerol. The most, rapidly labeled of the water-soluble deacylation products were galactosyl glycerol, digalactosyl glycerol, diglycerophosphate, sulfoglycosyl glycerol, and glycerophosphorylinositol. Labeling of the triglycerides proceeded more slowly than that of any of the surfactant lipids. Acid hydrolysis of the labeled galactolipids demonstrated active exchange of the galactose moieties with the intermediates of hexose photosynthesis and relatively slower labeling of the associated glycerol or fatty acids. However, the fatty acids of phosphatidylglycerol and the galactosyl diglycerides were more rapidly labeled than any other esterified fatty acids. Periodate oxidation of diglycerophosphate from phosphatidylglycerol indicated uniform labeling before 5 min. of steady-state photosynthesis. Possible metabolic sequences in the biosynthesis of the galactolipids and the phosphatides are discussed. The remarkable metabolic activity and high concentrations of phosphatidyl glycerol and the galactolipids in Chlorella attest to their importance in photosynthesis.