Serological Investigations of the Function of Galactolipids in the Thylakoid Membrane

Abstract

We investigated the influence of monospecific antisera to monogalactosyl diglyceride and to digalactosyl diglyceride on the photosynthetic electron transport in chloroplasts of higher plants. Both antisera inhibit the photoreduction of dichlorophenolindophenol (DCPiP) with water as the native electron donor as well as the reduction of anthraquinone-2-sulfonate with the electron donor couple DCPiP/ascorbate. The degree of inhibition of the galactolipid antisera in the region of photosystem I depends on the pH and the temperature of the reaction assay. Treatment of the chloroplasts with sodium periodate or with lipase results in a complete loss of any inhibition by the galactolipid antisera. Treatment with β-galactosidase, however, had no influence on the reactions with galactolipid antisera. The sites of inhibition of the galactolipid antisera could be localized on the donor side of photosystem I as well as on the donor side of photosystem II. From this we conclude that the mono- and digalactosyl diglyceride molecules that are localized on the stroma side of the membrane are components of the photosystem I- and also of the photosystem II-protein-lipid-complex. We may conclude that there are obviously interactions between the galactolipid molecules and the photosynthetically active proteins, since the binding of antibodies leads to a partial blocking of electron transport.