The Bakerian Lecture, 1977 - In vitro models for photosynthesis

Attempts to construct, in vitro , systems which imitate parts of the photosynthetic process serve two purposes. First, they may confirm, or not confirm, structures and mechanisms proposed on the basis of analyses of the living system. Second, they may lead to a purely photochemical system for the capture and storage of solar energy. For the latter purpose, the most interesting part of the photosynthetic process is photosystem II, in which water is split by visible light into oxygen and a reduced material. The principal stages of the process are probably ( a ) light harvesting and trapping, ( b ) electron transfer from chlorophyll to a quinone, and ( c ) oxidation of water via an intermediate containing manganese. Each of these three processes has now been reproduced to some extent in vitro but the light harvesting antenna efficiencies are lowered by concentration quenching. Recent progress, including kinetic investigations in the picosecond region and theoretical studies of energy transfer in the antenna are described.