Fourier transform infrared evidence for a ferric six-coordinate nitrosylheme b 3 complex of cytochrome cbb 3 oxidase from Pseudomonas stutzeri at ambient temperature

Abstract

We report the first vibrational study of NO bound to an oxidized heme-copper oxidase. Cytochrome cbb 3 oxidase from P. stutzeri reduces both O 2 and NO to H 2O and N 2O, respectively. The ferric nitrosyl complex of cbb 3 exhibits v(N-O) at 1903 cm -1. This frequency is very similar to v(NO) of nitric oxide reductase, the acidic form of Met Mb-NO, but 18 cm -1 lower than that of neutral Met Mb-NO. By monitoring the NO intensity, we estimate that NO dissociates from the heme b 3 pocket, without binding to Cu B, with k = 1.8 × 10 -3 s -1. Therefore, NO binding occurs at the heme site and not at Cu B, generating a nitrosonium Cu B 1+-NO + species as proposed recently (Torres; J.; Cooper, C.E.; Wilson, M.T. J. Biol. Chem. 1998, 273, 8756-8766). The coordination of NO to cbb 3 oxidase and to nitric oxide reductase and Mb is compared and discussed