Plant photosystem I--the most efficient nano-photochemical machine.

Hydrogen is one of the most promising energy carriers among environmentally friendly and clean energy sources for the future. If the extremely effective photosynthetic energy conversion could be efficiently combined with a biological process of hydrogen production, it will represent a significant step toward this goal. The best candidate to do the job is photosystem I (PSI) of oxygenic photosynthesis. Despite its enormous complexity, the plant PSI is arguably the most efficient nano-photochemical machine in Nature. It emerged as a homodimeric structure containing several chlorophyll molecules over 3.5 billion years ago, and has perfected its photoelectric properties ever since. The recently determined structure of plant PSI, which is at the top of the evolutionary tree of this kind of complexes, provided the first relatively high-resolution structural model of the supercomplex containing a reaction center (RC) and a peripheral antenna (LHCI) complexes. The structure should provide a template for designing artificial systems amenable for utilizable energy production.