Abstract

Electron-transfer rate constants of the single type I Cu protein pseudoazurin from Achromobacter cycloclastes with cytochrome c 551 from Pseudomonas aeruginosa and cytochrome c from bovine heart were determined to be (4.55 ± 0.01) x 10 5 M -1 s -1 and 384 ± 3 M -1 s -1 respectively at pH 7.0 (25°C) by the stopped-flow method, 1 = 0.1 M (NaCI). Using the Marcus equations, corresponding cross-reaction rate constants were calculated using the self-exchange rate constants and compared to the observed rate constants. The cross-reaction rate constants of pseudoazurin with Pseudomonas aeruginosa cytochrome c 551 and bovine heart cytochrome c were calculated to be 1.4 X 10 5 M -1 s -1 and 1.8 X 10 3 M -1 s -1 respectively. The pH effect on the reaction of pseudoazurin with bovine heart cytochrome c was investigated. The obtained kinetic parameters for the cytochrome c oxidation of reduced pseudoazurin estimated to be p K H = 6.5 ± 0.2, k o = 924 ± 77 M -1 s -1 (deprotonated form), and k H = 184 ± 52 M -1 s -1 (protonated form).

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