title: Calcium EXAFS establishes the Mn-Ca cluster in the oxygen-evolving complex of photosystem II.
abstract: The proximity of Ca to the Mn cluster of the photosynthetic water-oxidation complex is demonstrated by X-ray absorption spectroscopy. We have collected EXAFS data at the Ca K-edge using active PS II membrane samples that contain approximately 2 Ca per 4 Mn. These samples are much less perturbed than previously investigated Sr-substituted samples, which were prepared after Ca depletion. The new Ca EXAFS clearly shows backscattering from Mn at 3.4 A, a distance that agrees with that surmised from previously recorded Mn EXAFS. This result is also consistent with earlier related experiments at the Sr K-edge, using samples that contained functional Sr, that show Mn is approximately 3.5 A distant from Sr. The totality of the evidence clearly advances the notion that the catalytic center of oxygen evolution is a Mn-Ca heteronuclear cluster.
authors.affiliation: Physical Biosciences Division, Melvin Calvin Laboratory, Lawrence Berkeley National Laboratory, Berkeley, California 94720-5230, USA.
authors.forename: Roehl M
authors.initials: RM
authors.lastname: Cinco
authors.forename: Karen L
authors.initials: KL
authors.lastname: McFarlane Holman
authors.forename: John H
authors.initials: JH
authors.lastname: Robblee
authors.forename: Junko
authors.initials: J
authors.lastname: Yano
authors.forename: Shelly A
authors.initials: SA
authors.lastname: Pizarro
authors.forename: Emanuele
authors.initials: E
authors.lastname: Bellacchio
authors.forename: Kenneth
authors.initials: K
authors.lastname: Sauer
authors.forename: Vittal K
authors.initials: VK
authors.lastname: Yachandra
mesh_terms: D002118:Calcium / Q000737:chemistry*; D005583:Fourier Analysis; D008345:Manganese / Q000737:chemistry*; D016011:Normal Distribution; D010088:Oxidoreductases / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D011137:Polystyrenes / Q000737:chemistry; D011145:Polyvinyls / Q000737:chemistry; D012542:Scattering, Radiation; D013057:Spectrum Analysis / Q000379:methods / Q000706:statistics & numerical data; D018724:Spinacia oleracea / Q000201:enzymology; D014867:Water; D014965:X-Rays
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D011137:Polystyrenes; D011145:Polyvinyls; D014867:Water; D008345:Manganese; C006960:chelex; D010088:Oxidoreductases; D010100:Oxygen; D002118:Calcium