The phenomenon of UV-Vis spectroscopic changing due the binding of CO to the nitric oxide reductase from Bacillus Azotoformans

Abstract

Gram-positive bacterium, Bacillus azotoformans, possess a nitric oxide reductase named CuANOR (formerly qCuANOR). The purified enzyme consists of two subunits. On the basis of UV-Vis and EPR spectra, it was elucidated that its small subunit contains the mixed-valence dinuclear CuA center and its large subunit of CuANOR contains a low-spin heme b centre, a high-spin heme b and one nonheme iron centre. The latter two grouped is an EPR-silent binuclear iron centre where NO reduction occurred. The CuANOR revealed itself as a new class of nitric oxide reductase, a new member of cytochrome c oxidase superfamily. The structure of CuANOR is not available yet. Previous studies on Raman resonance and FTIR demonstrated the capability of both heme iron and non heme-iron to bind one CO molecule each in the highly free chloride of dithionite-reduced CuANOR, whereas at high chloride concentration the binding of CO at non-heme iron was lost. Whether the binding of CO to CuANOR is followed by the oxidation of CO to CO2, as found in cytochrome c oxidase, hemoglobin, myoglobin, and free heme, has never been reported. This paper reports the phenomenon of UV-Vis spectroscopic changing due the binding of CO to CuANOR which explain the enzyme reactivity toward CO molecule.