Chapter 35 Photosynthetic pigment-protein complexes in planar lipid membranes

Abstract

This chapter discusses the photosynthetic pigment–protein complexes in planar lipid membranes. The photosynthetic pigment–protein complexes may be classified into two separated and functionally distinctive classes: reaction centers (PS II, PSI and BRC) and light harvesting complexes (such as the largest light- harvesting complex of PS II, LHCII). Major part of research on photosynthetic pigment–proteins carried out with the application of model planar lipid membranes concerns the electron flow across the reaction centers, in particular BRC. The fact that the membrane separated two water bulk phases containing cytochrome c and ubiquinone, the secondary electron donors and acceptors to BRC, respectively, enabled the observation of light-induced electric current and voltage across the protein—containing membrane. The wavelength dependence of the photoresponse matched the absorption spectrum of reaction centers, which is a proof of functional reconstitution of the protein complex. The main physiological function of photosynthetic antenna complexes, such as LHCII, is harvesting light quanta and transferring excitation energy toward the reaction centers. According to the current knowledge these pigment–proteins are not directly involved in the linear or cyclic photosynthetic electron transfer in the thylakoid membranes.