Enzyme decay, hydrogen peroxide

Research conducted at Washington State University, as well as in situ applications by commercial entities, has indicated that stabilization of hydrogen peroxide is necessary for effective subsurface injection [39]. Without stabilization, added peroxide decomposes rapidly through interaction with iron oxyhydroxides, manganese oxyhydroxides, dissolved metals, and enzymes (e.g., peroxidase and catalase). Some of these peroxide decay pathways involve nonhydroxyl radical-forming mechanisms, and therefore are especially detrimental to Fenton oxidation systems. 

Yamazaki, Mason and Piette [63-65] have investigated the mechanism of action of peroxidases using flow ESR apparatus. The peroxidase used (from Japanese turnips) catalyses the oxidation of a number of substrates such as indoleacetic acid, dihydroxyfumarate and triose reductone by hydrogen peroxide. They were able to demonstrate directly the presence of free radical intermediates, a number of which could be identified from their hyperfine structure, and to show a correlation between ESR signal intensity and the kinetics expected for the reaction. This was strong evidence for a mechanism concerning one-electron transfer steps. The steady state concentration of free radicals was proportional to the square root of the enzyme concentration and the main decay route of the radicals was via dismutation. 

The first successful observation and characterization of the ascorbate free radical was carried out with ESR (14,15). A 1.7-G ESR doublet was reported and it was correctly concluded that the observed spectrum represented the anionic form (A ) of the radical. These measurements (14,15) showed that the enzyme-generated radical (horseradish peroxidase-hydrogen peroxide-ascorbate) was present as a free radical and decayed by second-order kinetics (see Figure 2). Recent experiments (16,17) have shown that ascorbate oxidase and dopamine-monooxygenase also generate unbound ascorbate radicals. 

The peroxides that activate these enzymes are produced internally by th biota or, alternatively, are produced externally, mainly by photochemical proc esses in the sea (72). Gschwend et al. (71), having found very little halocarboi in the interior tissues of macroalgae that produce these compounds, conclude" that much of the activity must be located in the surface tissues. This findin is consistent with the idea that extracellular peroxides are involved in th activation of these haloperoxidases. Moffett and Zafiriou (73) and Cooper am Zepp (74) provided evidence that peroxidases associated with aquatic particle in fresh water and coastal waters account for a large fraction of the decay o hydrogen peroxide, although it was not shown that haloperoxidases were re sponsible for the observed activity. 

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