Manganese ions, reactions

Metal-Catalyzed Oxidation. Trace quantities of transition metal ions catalyze the decomposition of hydroperoxides to radical species and greatiy accelerate the rate of oxidation. Most effective are those metal ions that undergo one-electron transfer reactions, eg, copper, iron, cobalt, and manganese ions (9). The metal catalyst is an active hydroperoxide decomposer in both its higher and its lower oxidation states. In the overall reaction, two molecules of hydroperoxide decompose to peroxy and alkoxy radicals (eq. 5). 

Discussion. In mixtures of magnesium and manganese the sum of both ion concentrations may be determined by direct EDTA titration. Fluoride ion will demask magnesium selectively from its EDTA complex, and if excess of a standard solution of manganese ion is also added, the following reaction occurs at room temperature ... 

The set of all intermediate steps is called the reaction pathway. A given reaction (involving the same reactants and products) may occur by a single pathway or by several parallel pathways. In the case of invertible reactions, the pathway followed in the reverse direction (e.g., the cathodic) may or may not coincide with that of the forward direction (in this example, the anodic). For instance, the relatively simple anodic oxidation of divalent manganese ions which in acidic solutions yields tetrava-lent manganese ions Mn +— Mn -l-2e , can follow these two pathways ... 

This enzyme [EC 2.5.1.17], also referred to as cob(I)-alamin adenosyltransferase or aquacob(I)alamin adeno-syltransferase, catalyzes the reaction of cob(I)alamin with ATP and water to produce adenosylcobalamin, orthophosphate, and pyrophosphate (or, diphosphate). A cofactor for this enzyme is manganese ion. 

The enzyme that catalyzes reaction 7 has been solubilized, 4" 141 and purified141 2000-fold. The enzyme activity is dependent on manganese ions. The enzymes catalyzing reactions 5 and 6 have not yet heen solubilized, purified, or separated, and, therefore, the substrate specificities indicated remain speculative. 

In eukaryotic cells, amphomycin inhibits the formation of GlcNAc-PP-Dol, Man-P-Dol, and Glc-P-Dol from their respective nucleotide esters of sugars and Dol-P.134,158,347,348 These reactions have in common the fact that they require manganese ions and Dol-P, but high concentrations of neither the ion nor the lipid phosphate were able to overcome these blocks. The transfer of preformed Man-P-Dol347 (and, pos-... 

Not surprisingly, both manganese ions are necessary for the catalase activity of arginase, as confirmed by metal replacement experiments in a mutant arginase. Indeed, whereas the hydrolytic reaction was restored upon binding one Cd2+ ion to form a heteronuclear MnCd enzyme, catalase activity was not [111]. 

This reaction is mediated by a cluster of four manganese ions (Mn2+) in PSII. 

Each of the four manganese ions cycles between Mn(II) and Mn(III) to generate the four electrons necessary. Had each pathway consisted of a single antenna and manganese centre the overall water cleaving reaction would take far longer and require a complex stepwise pathway consequently the entire photosynthetic... 

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