title: The effect of complex formation upon the reduction rates of cytochrome c and cytochrome c peroxidase compound II.
abstract: The effect of complex formation between ferricytochrome c and cytochrome c peroxidase (Ferrocytochrome-c:hydrogen peroxide oxidoreductase, EC 1.11.1.5) on the reduction of cytochrome c by N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), reduced N-methylphenazonium methosulfate (PMSH), and ascorbate has been determined at low ionic strength (pH 7) and 25 degrees C. Complex formation with the peroxidase enhances the rate of ferricytochrome c reduction by the neutral reductants TMPD and PMSH. Under all experimental conditions investigated, complex formation with cytochrome c peroxidase inhibits the ascorbate reduction of ferricytochrome c. This inhibition is due to the unfavorable electrostatic interactions between the ascorbate dianion and the negatively charged cytochrome c-cytochrome c peroxidase complex. Corrections for the electrostatic term by extrapolating the data to infinite ionic strength suggest that ascorbate can reduce cytochrome c peroxidase-bound cytochrome c faster than free cytochrome c. Reduction of cytochrome c peroxidase Compound II by dicyanobis(1,10-phenanthroline)iron(II) (Fe(phen)2(CN)2) is essentially unaffected by complex formation between the enzyme and ferricytochrome c at low ionic strength (pH 6) and 25 degrees C. However, reduction of Compound II by the negatively changed tetracyano-(1,10-phenanthroline)iron(II) (Fe(phen)(CN)4) is enhanced in the presence of ferricytochrome c. This enhancement is due to the more favorable electrostatic interactions between the reductant and cytochrome c-cytochrome c peroxidase Compound II complex then for Compound II itself. These studies indicate that complex formation between cytochrome c and cytochrome c peroxidase does not sterically block the electron-transfer pathways from these small nonphysiological reductants to the hemes in these two proteins.
mesh_terms: D001205:Ascorbic Acid / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism*; D003578:Cytochrome-c Peroxidase / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D007700:Kinetics; D008773:Methylphenazonium Methosulfate; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000378:metabolism*; D010618:Phenanthrolines; D010655:Phenylenediamines / Q000378:metabolism; D011485:Protein Binding
chemical_list: D003574:Cytochrome c Group; D010618:Phenanthrolines; D010655:Phenylenediamines; D008773:Methylphenazonium Methosulfate; D006418:Heme; D010544:Peroxidases; D003578:Cytochrome-c Peroxidase; D001205:Ascorbic Acid