The cytochrome cbb3 from Pseudomonas stutzeri displays nitric oxide reductase activity

Abstract

The cytochrome cbb₃ is an isoenzyme in the family of cytochrome c oxidases. This protein purified from Pseudomonas stutzeri displays a cyanide‐sensitive nitric oxide reductase activity (V_max=100±9 mol NO·mol ·min⁻¹ and K_m=12±2.5 µm), which is lost upon denaturation. This enzyme is only partially reduced by ascorbate, and readily re‐oxidized by NO under anaerobic conditions at a rate consistent with the turnover number for NO consumption. As shown by transient spectroscopy experiments and singular value decomposition (SVD) analysis, these results suggest that the cbb₃‐type cytochromes, sharing structural features with bacterial nitric oxide reductases, are the enzymes retaining the highest NO reductase activity within the heme‐copper oxidase superfamily.