Nitrite reductase(NiR) is a key enzyme in the natural nitrogen cycle that catalyzes the reduction of nitrite.Cu-NiR and cd_1-NiR,which are encoded by the nirK and nirS genes,respectively,are rate-limiting enzymes in denitrification.Although they have similar functions,their structures and cofactors are different.In addition,they exhibit different responses to different environmental gradients.The structural characteristics,microbial population distribution,and detection techniques of these two enzymes are reviewed in this report.Furthermore,the environmental factors that determine the expressi...
