The primary process of photosynthesis takes place in an integral membrane protein-pigment complex called the reaction center. Light produces a charge separation and initiates a set of electron transfer reactions that result in the reduction of the terminal acceptor, which is a ubiquinone (QB). QB becomes doubly reduced and protonated, leaves the reaction center and initiates the formation of the proton gradient that provides the driving force for ATP formation. The main questions associated with the primary processes are associated with electron and proton transfers. The kinetics and mechanisms of the electron transfer reaction and the mechanism of protonation of the doubly reduced QB, which is buried inside the reaction center and, therefore, not accessible to protons from the outside will be investigated. Protons reach reduced QB by a charge relay mechanism involving protonatable residues and water molecules. The problem is to identify the constituents of the proton transfer chain. Site directed mutagenesis and the high resolution X-ray structure is used to predict several possible pathways. To determine which of these is the most effective, the binding of divalent transition metals, which block proton transfer, will be used. By determining the position of the cations by X-ray diffraction, the point of entry of protons and hence the starting point of the dominant pathway can be identified.
The aim of this research is to contribute toward an understanding of the primary processes in photosynthesis, i.e., the mechanism of conversion of electromagnetic energy into chemical energy. This process is of utmost importance as it provides the energy for all life on Earth. The research is focused on the photosynthetic processes in purple bacteria (e.g. Rhodobacter sphaeroides). Photosynthetic bacteria, because of their relative simplicity provide an excellent model system to study photosynthesis. The findings are expected to be of general applicability to other biological systems and mechanisms, foremost to green plant photosynthesis and to other bioenergetic processes
