Details

Autor(en) / Beteiligte

• Cheung, Eddy
• English, Ann M

Titel

Reductions by ferrocytochrome c peroxidase: 5. Kinetics of ferricyanide reduction

Ist Teil von

• Canadian journal of chemistry, 1995-07, Vol.73 (7), p.1181-1186

Ort / Verlag

Ottawa, Canada: NRC Research Press

Erscheinungsjahr

1995

Link zum Volltext

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• The kinetics of reduction of ferricyanide by yeast ferrocytochrome c peroxidase (CPP II ) were investigated as a function of ionic strength in phosphate buffers at pH 7.0 and 25 ± 1 °C. The observed bimolecular rate constant (k 12 ) is 8.4 × 10 4  M −1 s −1 in 0.1 M phosphate. The dependence of the reaction rate on ionic strength indicates a change of −9 on the protein at pH 7.0, which is in good agreement with the total charge of −11 estimated for CCP II from its amino acid content. Substituting k 12 at infinite ionic strength into the Marcus cross relation yields an electron self-exchange rate constant for the Fe III /Fe II couple of CCP of 7.2 × 10 −5  M −1 s −1 . This value is over four orders of magnitude higher than that calculated for the Fe IV /Fe III couple of CCP from literature data for cross-reactions with ferrocyanide at pH 7.0. Possible reasons for the large difference in the two CCP values are discussed. Literature data also allowed values for various other heme proteins to be determined from their cross-reactions with ferricyanide. The calculated rate constants vary by eight orders of magnitude, and the variation of with protein structure suggests that the redox reactivity of ferrous heme proteins towards ferricyanide is dependent on the spin state and coordination of iron, as well as on the accessibility of the heme. Keywords: cytochrome c peroxidase, ferricyanide, Marcus cross relation, electron self-exchange.