NosReduktase

NosReduktase, also known as nitrous oxide reductase (NosZ), is an enzyme in the microbial denitrification pathway that catalyzes the four-electron reduction of nitrous oxide (N2O) to nitrogen gas (N2). This final step converts a potent greenhouse gas into inert nitrogen, helping close the nitrogen cycle.

Structure and mechanism: NosReduktase is a copper-containing metalloenzyme located mainly in the periplasm of many Gram-negative denitrifying bacteria. It features two copper centers, CuA and CuZ, that form the active site for N2O reduction. Electrons are supplied by the bacterial electron transport chain through periplasmic redox partners and transferred to N2O at the CuZ center, yielding N2 and completing denitrification. There are two major phylogenetic variants, NosZ clade I and clade II, which differ in maturation requirements and partner proteins but share the same catalytic reaction.

Distribution and ecology: NosReduktase is widespread among denitrifying bacteria and, in some contexts, non-denitrifying organisms. It is found in soil, sediment, freshwater, and wastewater environments, where it contributes to the fate of nitrogen and helps regulate nitrous oxide emissions in natural and engineered ecosystems.

Regulation and expression: nosZ expression is typically responsive to respiratory conditions, often upregulated under low oxygen levels and in the presence of nitrate or nitrite. Regulation varies among species and can involve regulatory systems that coordinate nosZ with other denitrification genes, reflecting the environmental conditions and microbial community.

Impact and relevance: By reducing N2O to N2, NosReduktase mitigates a significant greenhouse gas source from soils, manure management, and wastewater treatment. Understanding its activity helps explain spatial and temporal variations in N2O fluxes and informs strategies to limit atmospheric emissions.