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The Pseudomonas enzyme is a cytochrome, but the enzyme from Micrococcus halodenitrificans is an iron protein containing molybdenum. Reduced benzyl viologen and other dyes bring about the reduction of nitrate.
under nitrate-rich conditions, the nar and nap genes encoding a membrane-bound form and a periplasmic form of nitrate reductase, as well as NO-regulated genes encoding flavohaemoglobin, flavorubredoxin and hybrid cluster protein are induced following transition from the oxic to anoxic state, and 20% of nitrate consumed in steady-state is released as N2O when nitrite has accumulated to millimolar levels. The kinetics of nitrate consumption, nitrite accumulation and N2O production are similar to those of wild-type in nitrate-sufficient cultures of a nap mutant. Under nitrate-limited conditions, periplasmic enzyme nap, but not nar, is upregulated following transition from oxic to anoxic metabolism and very little N2O production was observedA combination of nitrate-sufficiency, nitrite accumulation and an active Nar-type nitrate reductase leads to NO and thence N2O production, and this can account for up to 20% of the nitrate catabolized
deletion of nap gene abolishes anaerobic growth and also delays aerobic growth in both nitrate and ammonium media. Deletion of nap gene severely impairs magnetite biomineralization and results in fewer, smaller, and irregular crystals during denitrification and also microaerobic respiration, probably by disturbing the proper redox balance required for magnetite synthesis. In contrast to the case for the wild type, biomineralization in nap deletion cells is independent of the oxidation state of carbon substrate