Effect of manganese on the nuclear magnetic relaxivity of water protons in chloroplast suspensions |
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Authors: | HH Robinson RR Sharp CF Yocum |
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Institution: | 1. Department of Chemistry The University of Michigan Ann Arbor, MI. 48109 USA;2. Division of Biological Sciences The University of Michigan Ann Arbor, MI. 48109 USA |
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Abstract: | Field dispersion profiles of the proton spin-lattice relaxation rate, T1?1, in chloroplast suspensions show a local maximum near 20 MHz, probably due to bound Mn(II); EDTA extraction eliminates, and MnCl2 addition restores, the paramagnetic relaxivity. Since neither treatment affects water oxidation, the Mn(II) site monitored appears to lie outside the water-splitting enzyme. Intense illumination almost totally suppresses the paramagnetic relaxivity through an electron-transport-dependent mechanism. Previous reports that chloroplast nuclear magnetic relaxivity varies cyclically in flash experiments require reevaluation in terms of the probable role of Mn(II) that is nonfunctional in water oxidation. |
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Keywords: | nmr nuclear magnetic resonance DCMU 3-(3 4-dichlorophenyl)-1 1-dimethylurea PS photosystem |
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