World Scientific
Skip main navigation

Cookies Notification

We use cookies on this site to enhance your user experience. By continuing to browse the site, you consent to the use of our cookies. Learn More
×

System Upgrade on Tue, May 28th, 2024 at 2am (EDT)

Existing users will be able to log into the site and access content. However, E-commerce and registration of new users may not be available for up to 12 hours.
For online purchase, please visit us again. Contact us at customercare@wspc.com for any enquiries.

A density functional investigation of hydrogen peroxide activation by high-valent heme centers: implications for the catalase catalytic cycle

    https://doi.org/10.1142/S1088424610002161Cited by:4 (Source: Crossref)

    Catalases employ a tyrosinate-ligated ferric heme in order to catalyze the dismutation of hydrogen peroxide to O2 and water. In the first half of the catalytic cycle, H2O2 oxidizes Fe(III) to the formally Fe(V) state commonly referred to as Compound I. The second half of the cycle entails oxidation of a second hydrogen peroxide molecule by Compound I to dioxygen. The present study employs density functional (DFT) calculations to examine the nature of this second step of the catalatic reaction. In order to account for the unusual choice of tyrosinate as an axial ligand in catalases, oxidation of hydrogen peroxide by an imidazole-ligated Compound I is also examined, bearing in mind that imidazole-ligated hemoproteins such as myoglobin or horseradish peroxidase tend to display little, if any, catalatic activity. Furthermore, in order to gauge the importance of the cation radical of Compound I in peroxide activation, the performance of Compound II (the one-electron reduced version of Compound I, formally Fe(IV)), is also examined. It is found that hydrogen peroxide oxidation occurs in a quasi-concerted manner, with two hydrogen-atom transfer reactions, and that the tyrosinate ligand is in no way required at this stage. We propose that the role of the tyrosinate is purely thermodynamic, in avoiding accumulation of the much less peroxide-reactive ferrous form in vivo – all in line with the predominantly thermodynamic role of the cysteinate ligands in enzymes such as cytochromes P450.

    Most comprehensive & up-to-date research on PORPHYRINS
    Handbook of Porphyrin Science now available in 46 volumes