Catalase models

Green calculated the low-lying electronic states of Cpd I for a catalase model, with phenolate as the proximal ligand. He found that the ground state had the LS it ... 

SHORT SURVEY OF CATALASE MODELS WITH METALLOPORPHYRINS... 

Sulfonated metalloporphyrins adsorbed on ion-exchange resins are good catalase models and they can be recycled with a limited loss of catalytic activity. Fe deuteroporphyrin linked to polylysine via the axial ligation of an amino side chain of the lysine residues can also catalyze the dismutation of hydrogen peroxide. ... 

In addition, complexes with low- and high-molecular weight amines (ethylene-diamine, triethylenetetramine, butylamine, poly(ethyleneimine)) were tested as catalase models [75]. The examined polymer-metal catalysts were nearly as effective as the catalase models. Pshezhetskii et al. [76] studied the mechanism of hydrogen peroxide decomposition by PAA-Fe complex in the presence of diethylenetriamine as a cofactor (see the lower scheme on p. 12). 

To gain insight into the mechanisms of these enzymes, a variety of Mn complexes that mimic the active site have been developed [28]. Dismukes and coworkers reported the first functional catalase model that exhibits high activity towards H2O2 decomposition even after turnover numbers of 1000, no loss of activity towards H2O2 decomposition was observed [29]. The dinuclear Mn -complex is based on ligand 1... 

Although, salen Mn complexes for therapeutic use were originally conceived as SOD mimetics, it soon became clear that EUK-8 also exhibited catalase activity, the ability to metabolize hydrogen peroxide (75). The catalase activity of EUK-8 was not unexpected, since Mn porphyrins had been studied as catalase models by the Meunier laboratory (16) and, like the porphyrins, salen ligands form stable complexes with Mn(III) (6). As described previously (77), similar to that of mammalian heme-iron based catalases (78), the catalase activity of salen Mn complexes is not saturable with respect to hydrogen peroxide. As has been reported for protein catalases (18), salen Mn complexes exhibit peroxidase activity, in the presence of an electron donor substrate, as an alternative to a catalatic pathway. This supports the analogy between the behavior of these mimetics and that of catalase enzymes, and is consistent with the following mechanistic scheme (76,17) ... 

Przyklenk, K. and Kloner, R.A. (1986). Superoxide dismutase plus catalase improve contractile function in the canine model of the stunned myocardium. Circ. Res. 58, 148-156. 

Animal models In rat acetic acid colitis the severity of inflammation can be decreased by methoxypolyethyleneglycohSOD, catalase, allopurinol and SAZ (Keshavarzian et al., 1990 Haydek et al.,... 

Furthermore, depletion of hepatic GSH induced chemically or by fasting augmented hepatic I/R-induced enzyme release and promoted lipid peroxidation (Jennische, 1984 Stein et al., 1991) Benoit et al. (1992) have used portacaval-shunted rats as a model of chronic hepatic ischaemia, and were able to show decreases in total levels of SOD and xanthine dehydrogenase, but no significant change in catalase or glutathione peroxidase. 

Steer, M.L., Rutledge, P.L., Powers, R.E., Saluja, M. and Saluja, A.K. (1991). The role of oxygen-derived fiee radicals in two models of experimental acute pancreatitis effects of catalase, superoxide dismutase, dimethyl sulphoxide, and allopurinol. Klin. Wochenschr. 69, 1012-1017. 

Catalase, the antioxidant enzyme that converts hydrogen peroxide to water, has been evaluated in combination with SOD in a model of focal ischaemic stroke in the rat. Both enzymes were eonjugated with polyethylene glycol to increase the circulatory half-life. They significantly reduced inferct volume (Liu et al., 1989). 

Meunier, B. Models of Heme Peroxidases and Catalases , Imperial College Press London, 2000 pp. 171-214. 

The kinetics of reactions of NO with ferri- and ferro-heme proteins and models under ambient conditions have been studied by time-resolved spectroscopic techniques. Representative results are summarized in Table I (22-28). Equilibrium constants determined for the formation of nitrosyl complexes of met-myoglobin (metMb), ferri-cytochrome-c (Cyt111) and catalase (Cat) are in reasonable agreement when measured both by flash photolysis techniques (K= konlkQff) and by spectroscopic titration in aqueous media (22). Table I summarizes the several orders of magnitude range of kon and kQs values obtained for ferri- and ferro-heme proteins. Many k0f[ values were too small to determine by flash photolysis methods and were determined by other means. The small values of kQ result in very large equilibrium constants K for the... 

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