Free radical enzymatic generation

In this chapter the generation of free radicals, mainly superoxide and nitric oxide, catalyzed by prooxidant enzymes will be considered. Enzymes are apparently able to produce some other free radicals (for example, HO and N02), although their formation is not always rigorously proved or verified. The reactions of such enzymes as lipoxygenase and cyclooxygenase also proceed by free radical mechanism, but the free radicals formed are consumed in their catalytic cycles and probably not to be released outside. Therefore, these enzymes are considered separately in Chapter 26 dedicated to enzymatic lipid peroxidation. 

Activation of the wood surface using enzymatic means to generate surface free radicals. 

Dinuclear iron centres occur in several proteins. They either bind or activate dioxygen or they are hydrolases. Ribonucleotide reductase (RR) of the so-called class I type contains one such centre in the R2 protein in combination with a tyrosyl radical, both being essential for enzymatic activity which takes place in the R1 protein subunit. The diiron centre activates dioxygen to generate the tyrosyl radicals which in turn initiate the catalytic reaction in the R1 subunit. The interplay between the tyrosyl free radical in R2 and the formation of deoxyribonucleotides in R1 which also is proposed to involve a protein backbone radical is a topic of lively interest at present but is outside the scope of this review. Only a few recent references dealing with this aspect are mentioned without any further discussion.158 159 1 1,161... 

Simpson, J. A., Gieseg, S. P, and Dean, R. T., Free radical and enzymatic mechanisms for the generation of protein bound reducing moieties. Biochim. Biophys. Acta 1156, 190-196 (1993). 

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