Lipid-Linked Desaturation of Palmitic Acid in Monogalactosyl Diacylglycerol in the Blue-Green Alga (Cyanobacterium) Anabaena variabilis Studied in Vivo

The mechanism of desaturation of palmitic acid in monogalactosyldiacylglycerol in Anabaena variabilis was studied by labelingin vivo with ¹³C and mass spectrometry. When the cells werefed with ¹³C]Na₂CO₃ for 2.5 h, 19% of the palmitic, but virtuallynone of the palmitoleic, acid at the C-2 position of the lipidwas enriched with ¹³C. During subsequent incubation for 7.5h, the ¹³C]palmitic acid was desaturated to ¹³C]palmitoleicacid. Mass spectrometric analysis of the 2-acylglycerol moietyof the lipid indicated that ¹³C]palmitoyl-¹³C]glycerol and¹²C]palmitoyl-¹²C]glycerol were converted to ¹³C]palmitoleoyl-¹³C]glyceroland ¹²C]palmitoleoyl-¹²C]glycerol, respectively. These resultssuggest that the palmitic acid was converted to palmitoleicacid in vivo by lipid-linked desaturation but not via a pathwayconsisting of deacylation, desaturation and reacylation. ⁴Present address: Department of Botany, Faculty of Science,University of Tokyo, Hongo, Tokyo 113, Japan ⁵Present address: Department of Physiological Chemistry andNutrition, Faculty of Medicine, University of Tokyo, Hongo,Tokyo 113, Japan (Received December 7, 1985; Accepted April 16, 1986)