title: The mechanism of reduction of single-site redox proteins by ascorbic acid.
abstract: The reduction of single-site haem and copper redox proteins by ascorbic acid was studied as a function of pH. Evidence is presented that indicates that the double-deprotonated ascorbate anion, ascorbate2-, is the reducing agent, and the pH-independent second-order rate constants for reduction by this species are given. Investigation of the temperature dependences of these rate constants have yielded the values of the activation parameters (delta H++ and delta S++) for reduction. These values, together with ligand-replacement studies, suggest that ascorbate2- acts as an outer-sphere reductant for these proteins. Reasons to account for the apparent inability of ascorbic acid to reduce the alkaline conformer of mammalian ferricytochrome c are suggested.
mesh_terms: D001205:Ascorbic Acid / Q000378:metabolism*; D001400:Azurin / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000378:metabolism; D007700:Kinetics; D008956:Models, Chemical; D010084:Oxidation-Reduction; D011485:Protein Binding; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D003574:Cytochrome c Group; D007093:Imidazoles; D001400:Azurin; D001205:Ascorbic Acid