Structure–function relationships of copper-containing nitrite reductases

Abstract

Dissimilatory nitrite reductase (NIR) is a key enzyme in the anaerobic respiratory pathway of denitrifying bacteria. There are two types of NIR, one of which contains copper and the other heme. Cu-containing NIR (Cu NIR) has the trimeric structure with one type 1 Cu (blue copper) atom and one type 2 Cu (nonblue copper) atom in each subunit. The type 1 Cu atom bound by 2His, Cys, and Met accepts one electron from an electron donor protein and shows an intense color, blue or green. The type 2 Cu atom bound by 3His and a solvent (H 2O or OH −) is a reduction center of nitrite to NO. The intramolecular long-range electron transfer process is observed from the type 1 site to the type 2 Cu site with a half-life period of ca. 0.3 ms. The present review deals with (i) spectroscopic characterization of Cu NIR’s, (ii) structures of Cu NIR’s, and (iii) functions of Cu NIR’s (intermolecular electron transfer process, intramolecular electron transfer process, and reduction of nitrite ion).