Proximity of calcium to the manganese cluster of the photosynthetic oxygen-evolving complex determined from strontium XAFS

摘要

Working on Photosystem II membranes from spinach, we substituted strontium for calcium and probed using Sr EXAFS for any nearby Mn. Sr EXAFS results indicate major differences between the functional (intact) and inactive (hydroxylamine-treated) samples. In intact samples, the Fourier transform of the Sr EXAFS shows a major peak that is missing in inactive samples. This interaction is best simulated by two Mn neighbors at a distance of ~3.5 Å.