Structure, Function, Regulation and Evolution of the Nitrite and Nitrous Oxide Reductases: Denitrification Enzymes With a Beta-Propeller Fold
Rob J.M. van Spanning
from: Nitrogen Cycling in Bacteria: Molecular Analysis (Edited by: James W. B. Moir). Caister Academic Press, U.K. (2011)
Specialized denitrifiers recruit 2 β-propeller enzymes in their anaerobic nitrate respiratory electron transfer network, one of which is an iron containing cd1-type nitrite reductase, termed NirS, and the other is a copper containing nitrous oxide reductase, NosZ. Together they complement a full denitrification pathway along with nitrate and nitric oxide reductases for the sequential reduction of nitrate to dinitrogen gas. These enzymes are tightly controlled on the level of expression and activity not only according to an energetic hierarchy but also to ensure a balanced conversion of the N-oxides and to prevent the accumulation of the toxic intermediates nitrite and nitric oxide. The adaptive response during the switch from aerobic respiration to denitrification is orchestrated by a dedicated signal transduction network that integrates environmental and intracellular signals and passes these on to the DNA. Amongst these signals are oxygen, denitrification intermediates (nitrate, nitrite, nitric oxide), the redox state of the respiratory components, and metal availability (copper, iron). The coordinate acquisition of these metals during the oxic-anoxic shift is a challenge since their bioavailability requires different reduction states and oxygen tensions read more ...