Iron-bound hydroxyl radical

In the field of enzyme catalysis, heme-proteins such as cytochrome P450, for example, exhibit both types of 0-0 bond cleavages in organic hydroperoxides and peroxy acids (178). Heterolytic cleavage of HOOH/ROOH yields H20 or the corresponding alcohol, ROH and a ferryl-oxo intermediate (Scheme 4). Homolytic 0-0 bond cleavage results in the formation of a hydroxyl (HO ) or an alkoxyl (RO ) radical and an iron-bound hydroxyl radical. 

In the next step of the reaction cycle, the enzyme-product compound (T) is formed by radical recombination of the iron-bound hydroxyl radical and the substrate radical. Finally, the product is released in the rate-limiting step (31) of the reaction. This step is also dependent on MMOB, and the cycle is complete. It is possible that compounds P, K, Q, and R all have an additional oxygen-derived bridge in addition to the hydroxo bridge. Thus, compounds P and K would have one /i-peroxo and one /a-hydroxo bridge, and compounds Q and R could have one fi-hydroxo and one ix-oxo bridge each [cf (122b, 10, 31)]. 

Fig. 4.18 An alternative meehanism is available for hydroxylation of a earbon adjaeent to a nitrogen atom. This meehanism is initiated by eleetron transfer fiom the nitrogen to compound I, forming a nitrogen radical cation and compound II. Proton removal and recombination with the iron-bound hydroxyl of compound II then yields the hydroxylated product. The high electronegativity of the...

The hydroxylation of single- and double-stranded DNA are changes characteristic of free-radical attack (reviewed by Winyard et al., 1992). An important mechanism is site-specific OH generation, catalysed by iron bound to... 

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