title: Water proton relaxation as a monitor of membrane-bound manganese in spinach chloroplasts.
abstract: First measurements of proton relaxation on chloroplast membranes are presented here. Experiments show that the water proton spin-lattice relaxation rate in chloroplast thylakoid membrane suspensions can be used to monitor membrane-bound manganese. The relaxation effect is reduced to 0.4 of its original value upon manganese extraction by washing with either alkaline Tris buffer or NH2OH/EDTA solution. Large increases in the proton relaxation rate are measured in the presence of reductants such as tetraphenylboron and NH2OH; oxidants such as potassium ferricyanide or 2,6-dichlorophenolindophenol lead to an decrease in this rate. These results suggest that manganese exists as a mixture of oxidation states in dark-adapted chloroplasts.
mesh_terms: D015086:2,6-Dichloroindophenol; D002462:Cell Membrane / Q000032:analysis / Q000648:ultrastructure; D002736:Chloroplasts / Q000032:analysis* / Q000648:ultrastructure; D004578:Electron Spin Resonance Spectroscopy; D005292:Ferricyanides; D007700:Kinetics; D008345:Manganese / Q000032:analysis*; D008433:Mathematics; D010944:Plants; D013696:Temperature; D014867:Water
chemical_list: D005292:Ferricyanides; D014867:Water; D008345:Manganese; D015086:2,6-Dichloroindophenol