Production of dioxygen in the dark: Dismutases of oxyanions

Abstract

O2-generating reactions are exceedingly rare in biology and difficult to mimic synthetically. Perchlorate-respiring bacteria enzymatically detoxify chlorite (ClO2-), the end product of the perchlorate (ClO4-) respiratory pathway, by rapidly converting it to dioxygen (O2) and chloride (Cl-). This reaction is catalyzed by a heme-containing protein, called chlorite dismutase (Cld), which bears no structural or sequence relationships with known peroxidases or other heme proteins and is part of a large family of proteins with more than one biochemical function. The original assumptions from the 1990s that perchlorate is not a natural product and that perchlorate respiration might be confined to a taxonomically narrow group of species have been called into question, as have the roles of perchlorate respiration and Cld-mediated reactions in the global biogeochemical cycle of chlorine. In this chapter, the chemistry and biochemistry of Cld-mediated O2 generation, as well as the biological and geochemical context of this extraordinary reaction, are described.