Mystery of distorted-chair structure in photosynthesis clarified
In photosynthesis in algae and higher plants, water is split into oxygen gas and hydrogen ions.
In Mn4CaO5, a complex, natural catalyst in photosynthetic protein Photosystem II (PSII), the bonds between manganese (Mn) and oxygen (O) atoms are elongated causing it to have a structure resembling that of a distorted chair. It is known that the distortion plays an important role in catalytic activity in water splitting; however, the snail-paced clarification of what role the distortion plays has hindered the development of efficient artificial photosynthesis.
A group of researchers led by Professor Hiroshi ISHIKITA and Assistant professor Keisuke SAITO (Graduate School of Science, Osaka University), by employing combined quantum mechanics/molecular mechanics (QM/MM) calculation methods, succeeded in revising the accepted idea that the presence of Ca distorted the structure. (This year’s Nobel Prize in Chemistry was awarded for QM/MM calculation.)
This group has clarified that the direct cause of the distortion was not Ca located in the seat of the chair-like structure, but Mn located in the back of the chair-like structure.
This achievement is expected to accelerate the development of artificial photosynthesis.
Professor Hiroshi ISHIKITA, conducted research at the University of Southern California through 2008 as a post-graduate researcher for this year’s Nobel Prize in Chemistry awardee Professor Arieh Warshel.