Effect of monogalactosyldiacylglycerol and other thylakoid lipids on violaxanthin de-epoxidation in liposomes

In this study we present evidence that one of two reactions of the xanthoph yll cycle, violaxanthin de-epoxidation, may occur in unilamellar egg phosph atidylcholine vesicles supplemented with monogalactosyldiacylglycerol (MGDG ). Activity of violaxanthin de-epoxidase (VDE) in this system was found to be strongly dependent on the content of MGDG in the membrane; however, only to a level of 30 mol%. Above this concentration the rate of violaxanthin d e-epoxidation decreased. The effect of individual thylakoid lipids on VDE-i ndependent violaxanthin transformation was also investigated and unspecific effects of phosphatidylglycerol and sulphoquinovosyldiacyglycerol, probabl y related to the acidic character of these lipids, were found. The presente d results suggest that violaxanthin de-epoxidation most probably takes plac e inside MGDG-rich domains of the thylakoid membrane. The described activit y of the violaxanthin de-epoxidation reaction in liposomes opens new possib ilities in the investigation of the xanthophyll cycle and may contribute to a better understanding of this process.