Crystallographic Structures of Nitrite Reductase and its Substrate Bound Complex

Abstract

Dissimilatory nitrite reductase (NiR) is a key enzyme in the anaerobic respiratory pathway of denitrifying bacteria where nitrate is sequentially reduced to the gaseous products NO, N2O or N2, leading to a significant loss of fixed nitrogen from the terrestrial environment (Payne, 1985). The NiR from Alcaligenes xylosoxidans (AxNiR) (Abraham et al., 1993) belongs to the group of NiRs which utilise copper at the redox active centres. All Cu NiRs isolated so far have a strong band near 600nm arising from a (Cys)S → Cu (II) charge transfer which is characteristic of a type 1 Cu centre. The ratio of intensity of this band to a second charge transfer absorption band at ∼460nm determines whether a Cu NiR is blue or green in colour (Han et al., 1993). AxNiR belongs to the subset of Cu-NiRs which are blue in colour and are thought to have azurin as the electron partner.