Peroxidative enzyme

Further work by Stevenson et al. [105] has shown that 16a-hydroxytestosterone can be aromatized to oestriol via the 19-dihydroxy and 19-oxo derivatives, these changes being identical to those indicated above [104], in which an enzyme-peroxide intermediate was postulated (Fig. 14). Since the aromatase system is known to be catalysed by cytochrome P-450 [106], it is feasible that involvement of a P-450-peroxide species could be envisaged, not only in the C-10,19 cleavage but also in the preceding hydroxylations (Fig. 15). 

Miller MA, Shaw A, Kraut J (1994) 2.2 A structure of oxy-peroxidase as a model for the transient enzyme peroxide complex. Nat Struct Mol Biol 1 524—531... 

When threatened, the bombardier beetle mixes hydroquinone and H202 with enzymes. Peroxide oxidizes hydroquinone to quinone, and the strongly exothermic reaction heats the solution to boiling. The hot, irritating liquid sprays from the tip of the insect s abdomen. 

A plausible rationalization of our observations is the formation of an enzyme-peroxide complex at the type 3 site. The fact that it is fully formed even at rather low concentrations of reagents (2 X 10 6 M in each) and the stability observed over many hours in the presence of highly efficient and specific catalysts for peroxide decomposition require an exceptional affinity of interaction. 

By analogy to other catalase-ligand interactions. Compound I was initially taken to be an enzyme-peroxide complex, even if a rather unusual one. However, the optical spectrum of Compound I 154, 1 5), its magnetic susceptibility (156), and the lack of a discernible EPR signature 126b) are unlike those of other high- or low-spin catalase-ligand derivatives. 

A relationship between ki, pp and van der Waals volumes of peroxides is the only discernible pattern. This strongly suggests that enzyme-peroxide association is the rate-determining step and, as such, is rather irrelevant to the elucidation of the redox transformations. 

All such suggestions are clearly most tentative since the nature of the oxidation product. Compound I, is still unresolved. The stoichiometry of the enzyme-peroxide reaction merely demands that its formal oxida-... 

Demir, A., Aiik, B., Ozdogan, E., Seventekin, N., 2010. The comparison of the effect of enzyme, peroxide, plasma and chitosan processes on wool fabrics and evaluation for antimicrobial activity. Fibers Polym. 11, 989-995. 

The source of initiation has also been shown by Palozza et al. (77) to modify tocopherol s effectiveness as an antioxidant. Three types of initiation were studied on rat liver microsomes by these investigators and they included enzymic peroxidation induced by NADPH, ADP and iron the water-soluble azo compound... 

RAPID ENZYMIC PEROXIDATION OF POLYUNSATURATED FATTY ACIDS ON HYDRATION OF WHEAT MILLING PRODUCTS... 

The formation of eicosanoids is an example of tightly controlled enzymic peroxidation of lipids. Peroxidation reactions can also occur chemically and unless controlled by the presence of natural antioxidant systems can give rise to massive cell damage, disintegration and disease. The chemistry involved is discussed in Chapter 3, while the pathological implications are described in Chapter 8. 

As suggested above, the reaction can be divided into two phases first the peroxide reacts with enzyme to form enzyme peroxide compounds, and then the peroxide compounds, DHF, and oxygen react to destroy the peroxide compound, oxidize the DHF, and regenerate the peroxide from oxygen. The theories of Chance (1952a), Mason (1958), and Yamazaki (1958) differ in their interpretation of this second reaction. These theories will be discussed in Section II.E, following an analysis of some other aspects of the oxidatic reaction. 

---