Electron-transfer reactions superoxide dismutase models

Carloni et al.91 applied the DFT(PZ) calculations to investigate the electronic structure of various models of oxydized and reduced Cu, Zn superoxide dismutase. The first stage of the enzymatic reaction involves the electron transfer from Cu" ion to superoxide. The theoretical investigations provided a detailed description of the electronic structure of the molecules involved in the electron transfer process. The effect of charged groups, present in the active center, on the electron transfer process were analyzed and the Argl41 residue was shown to play a crucial role. 

Cu,Zn superoxide dismutase. Essentially, these observations support a stepwise one-electron model again. Interestingly, the oxidation state of copper does not change during the catalytic reaction, i.e. the sole kinetic role of the histidine coordinated metal center is to alter the electronic structures of the substrate and 02 in order to facilitate the electron transfer process between them. 

Manganese compounds of biologic importance are examined by pulse radiolysis e.g., the rate of dismutation of radiation-generated Of is catalyzed by Escherichia coli, Mn-containing superoxide dismutase involving electron transfer in which enzymes with Mn(IV), Mn(IIl), Mn(II) and Mn(I) oxidation states are involved. A kinetic model for the reaction mechanism of an Mn dismutase from Bacillus stearothermophilus accounts for the variation of the rate of decay on the concentrations of Oj, enzyme, HjOj, NaNj, KCN and H+. 

---