Nitric oxide activation by caa3 oxidoreductase from Thermus thermophilus

Abstract

Visible and UV-resonance Raman spectroscopy was employed to investigate the reaction of NO with cytochrome caa3 from Thermus thermophilus. We show the formation of the hyponitrite (HO–N[double bond, length as m-dash]N–O)− bound to the heme a3 species (νN[double bond, length as m-dash]N = 1330 cm−1) forming a high spin complex in the oxidized heme a3 Fe/CuB binuclear center of caa3-oxidoreductase. In the absence of heme a3 Fe2+–NO formation, the electron required for the formation of the N[double bond, length as m-dash]N bond originates from the autoreduction of CuB by NO, producing nitrite. With the identification of the hyponitrite intermediate the hypothesis of a common phylogeny of aerobic respiration and bacterial denitrification is fully supported and the mechanism for the 2e−/2H+ reduction of NO to N2O can be described with more certainty.