Catalytic Activity of the Manganese and Iron Enzymes

2 Catalytic Activity of the Manganese and Iron Enzyme Due to the uncomplete knowledge of the active centers of iron and mangano superoxide dismutases, only limited informations of the catalytic activities are available. It was demonstrated with nuclear magnetic relaxation techniques that the iron 

Examination of the pH-dependence showed that the dissoziation constant of azide is influenced by a ionizing group near the iron having a pK of 8.7. The coordination of this anion to Fe(III) is thought to be preceded by an association with a non-chromophoric site on the protein which was termed anion binding pocket . 

In contrast to bovine Cu2Zn2- and iron superoxide dismutase from P. leiognathi, the iron enzyme from E. coli exhibits saturation kinetics during catalytic action A group which ionizes with a pK, = 8.8 was found to be responsible for this phenomenon. For the dismutation of superoxide by iron SOD s a ruction scheme is proposed which includes alternate r uction-oxidation of the metal  

This catalytic scheme is very similar to that of Cu2Zn2Superoxide dismutases. The iron enzymes from E. coli, A. vinelandii and P. ovalis display redox potentials of 0.27 V In contrast to the other SOD s, the reduction potentials of Fe-proteins decrease when the pH is raised from pH 6.0 to 9.0. It was assumed that the reduction of Fe(III) cau a proton to be bound below pH 9.0, which is not observed above this pH-value. 

3 Low Molecular Weight Compounds Mimicking Superoxkie Dismutase Activity 

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