Photooxidation and Pheophytin Formation of Chlorophyll in the Light-Harvesting Chl-a/b-Protein Complex Exposed to Fatty Acids: Protective Role of the Intact Apoprotein

Abstract

Pure chlorophylls (Chl) in organic solution are readily bleached in the light or converted to pheophytin at low pH. When organized in the light-harvesting Chl-a/b-protein complex of Photosystem II (LHC), however, they are stable under light (1) and under strongly acidic conditions (2). Photo- and acid stability of the LHC-bound pigments are destroyed in presence of the amphiphilic detergent Triton X-100 and of the lipophilic terpene limonene (1). Photodestruction of the pigments in Triton- or limonene-treated LHC requires O2 and is prevented under anaerobic conditions. These observations suggest that the LHC apoprotein plays an important role in protecting the Chls from the destructive action of O2 and H+ (1). In the present study the LHC is exposed to fatty acids of increasing hydrocarbon chain length. It is asked whether fatty acids destabilize the LHC and whether destabilization requires a minimal length of the lipophilic hydrocarbon chain.