Nonredox di-Mn Enzymes — Arginase

In addition to the redox di-Mn catalases, there are a number of other enzymes with di-Mn centres, of which the best characterised are arginases, which catalyse the divalent cation-dependent hydrolysis of L-arginine to form L-omithine (Ash, 2004) and urea. 

FIGURE 16.7 Catalytic reaction cycle for manganese catalase turnover. (Adapted from Whittaker, Baryrun, Igarashi, Whittaker, 2003.) 

Mn(II) centre (c, d) Following a proton transfer to the leaving amino group mediated by Asp 128, the tetrahedral intermediate collapses to yield the products L-ornithine and urea, (e) A water molecule enters to bridge the binuclear Mn cluster, causing the urea product to move to a terminal coordination site on Mn. Product dissociation facilitates ionisation of the metal-bridging water molecule to yield the catalytically active hydroxide ion. Proton transfer from the metal-bridging water to the bulk solvent is mediated by His-141, followed by the release of the two products. 

(2004). Arginine metabolism enzymology, nutrition and clinical significance. Journal of Nutrition, 134, 2760S—2764S. 

Barber, J. (2008). Photosynthetic generation of oxygen. Philosophical Transactions of the Royal Society B Biological Sciences, 363, 2665-2674. 

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Introduction Mn Chemistry and Biochemistry Photosynthetic Oxidation of Water — Oxygen Evolution Mn and Detoxification of Oxygen Free Radicals Nonredox di-Mn Enzymes — Arginase... 

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