Electron-transfer reactions of blue copper protein pseudoazurin from Achromobacter cycloclastes with cytochromes

Electron-transfer rate constants of the single type 1 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 degrees C) by the stopped-flow method, I = 0.1 M (NaCl). 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 pK(H) = 6.5 +/- 0.2, k(0) = 924 +/- 77 M(-1)s(-1) (deprotonated form), and k(H) = 184 +/- 52 M(-1)s(-1) (protonated form). (C) 1997 Elsevier Science S.A.