Proton-coupled electron transfer promotes the reduction of ferrylmyoglobin by uric acid under physiological conditions

Author(s)

de Zawadzki, Andressa ; Cardoso, Daniel R. ; Skibsted, Leif H.

• Document type: Journal article
• Source: RSC ADVANCES; v. 7, n. 29, p. 17824-17831, 2017.
• Web of Science Citations: 2

Abstract

The hypervalent muscle pigment ferrylmyoglobin, MbFe((IV))] = O, is not reduced by urate monoanions at physiological conditions despite a strong driving force of around -30 kJ mol(-1) while for low pH, uric acid was found to reduce protonated ferrylmyoglobin, MbFe((IV))] O, H+, efficiently in a bimolecular reaction with k(1) = 1.1 +/- 0.1-10(3) L mol(-1) s(-1), Delta H-double dagger = 66.1 +/- 0.1 kJ mol(-1) and Delta S-double dagger = 35.2 +/- 0.2 J mol(-1) K-1. For intermediate pH, like for anaerobic muscles and for meat, proton-coupled electron transfer occurs in a transition state, [MbFe(IV)] = O...H+... urate](double dagger), which is concluded to be formed from uric acid and MbFe((IV))] = O rather than from urate and MbFe(IV)] = O, H+ with k(3) = 9.7 +/- 0.6-10(2) L mol(-1) s(-1), Delta H-double dagger = 59.2 +/- 0.1 kJ mol(-1) and Delta S-double dagger = 11.5 +/- 0.3 J mol(-1) K-1. The activation parameters as calculated from the temperature dependence of the pH-reduction profile in aqueous 0.067 mol L-1 NaCl (from 25 degrees C up to 40 degrees C), support a mechanism for reduction of hypervalent heme iron, where initial proton transfer to oxo-iron initiates the intermolecular electron transfer from urate to ferrylmyoglobin. The concentration of the powerful prooxidant ferrylmyoglobin increases strongly during digestion of red meat in the stomach. A concomitant increase in uric acid concentration may serve as an inherent protection against radical formation by ferrylmyoglobin. (AU)

• FAPESP's process: 11/51555-7 - Bread and meat for the future
• Grantee: Daniel Rodrigues Cardoso
• Support Opportunities: Regular Research Grants