期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 99, 期 13, 页码 8631-8636出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.132266199
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资金
- NIGMS NIH HHS [R56 GM055302, GM-55302, R01 GM055302] Funding Source: Medline
The photosynthetic water oxidation complex consists of a cluster of four Mn atoms bridged by O atoms, associated with Ca2+ and Cl-, and incorporated into protein. The structure is similar in higher plants and algae, as well as in cyanobacteria of more ancient lineage, dating back more than 2.5 billion years ago on Earth. It has been proposed that the proto-enzyme derived from a component of a natural early marine manganese precipitate that contained a CaMn4O9 cluster. A variety of MnO2 minerals are found in nature. Three major classes are spinels, sheet-like layered structures, and three-dimensional networks that contain parallel tunnels. These relatively open structures readily incorporate cations (Na+, Li+, Mg2+, Ca2+, Ba2+, H+, and even Mn2+) and water. The minerals have different ratios of Mn(III) and Mn(IV) octahedrally coordinated to oxygens. Using x-ray spectroscopy we compare the chemical structures of Mn in the minerals with what is known about the arrangement in the water oxidation complex to define the parameters of a structural model for the photosynthetic catalytic site. This comparison provides for the structural model a set of candidate Mn-4 clusters-some previously proposed and considered and others entirely novel.
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