Redox Equilibria in Hydroxylamine Oxidoreductase. Electrostatic Control of Electron Redistribution in Multielectron Oxidative Processes
Citations Over TimeTop 16% of 2005 papers
Abstract
We report results of continuum electrostatics calculations of the cofactor redox potentials, and of the titratable group pK(a) values, in hydroxylamine oxidoreductase (HAO). A picture of a sophisticated multicomponent control of electron flow in the protein emerged from the studies. First, we found that neighboring heme cofactors strongly interact electrostatically, with energies of 50-100 mV. Thus, cofactor redox potentials depend on the oxidation state of other cofactors, and cofactor redox potentials in the active (partially oxidized) enzyme differ substantially from the values obtained in electrochemical redox titration experiments. We found that, together, solvent-exposed heme 1 (having a large negative redox potential) and heme 2 (having a large positive redox potential) form a lock for electrons generated during the oxidation reaction The attachment of HAO's physiological electron transfer partner cytochrome c(554) results in a positive shift in the redox potential of heme 1, and "opens the electron gate". Electrons generated as a result of hydroxylamine oxidation travel to heme 3 and heme 8, which have redox potentials close to 0 mV versus NHE (this result is in partial disagreement with an existing experimental redox potential assignment). The closeness of hemes 3 and 8 from different enzyme subunits allows redistribution of the four electrons generated as a result of hydroxylamine oxidation, among the three enzyme subunits. For the multielectron oxidation process to be maximally efficient, the redox potentials of the electron-accepting cofactors should be roughly equal, and electrostatic interactions between extra electrons on these cofactors should be minimal. The redox potential assignments presented in the paper satisfy this general rule.
Related Papers
- → Cytochrome cd1 from Paracoccus pantotrophus Exhibits Kinetically Gated, Conformationally Dependent, Highly Cooperative Two-Electron Redox Behavior(2000)47 cited
- → Interplay and Competition Between Two Different Types of Redox‐Active Ligands in Cobalt Complexes: How to Allocate the Electrons?(2022)6 cited
- → Complexity in the redox titration of the dihaem cytochrome c4(1985)33 cited
- → Calculating Equilibrium Potentials of Solutions Containing Several Redox Couples(2012)3 cited
- → Redox Reactions in Non‐Aqueous Solvents(2002)8 cited