"Nature figured out how to split water using sunlight in an energy-efficient way 2.5 billion years ago," says study co-author Jim Barber of Imperial College London. "By revealing the structure of the water-splitting center we can begin to unravel how to perform this task in an energy-efficient way, too." Barber and his colleagues used x-ray crystallography to take the highest-resolution image yet of the catalyst essential to the photosystem II complex in plants, which enables photosynthesis. The scientists analyzed a plant bacterium known as Thermosynechococcus and determined that the complex comprises four manganese atoms, four oxygen atoms and a calcium atom arranged as a cube, with the most reactive manganese atom attached to a corner oxygen. "Our structure also reveals the position of key amino acids, the building blocks of proteins, which provide details of how cofactors are recruited into the reaction center," says team member So Iwata of Imperial College and Japan Science and Technology Corporation.
The current method of splitting water into its component parts, electrolysis, is much more costly than both natural gas and gasoline and is therefore not a feasible route to hydrogen fuel. The new work could help lower such barriers. "Manufacturing hydrogen from water using the photosynthetic methods would be far more efficient than using electrolysis," Barber says, "and if we can learn how to use even a fraction of the 326 million cubic miles of water on the planet we can begin to address the world¿s pressing need for new and environmentally friendly energy sources."