TABLE 1.

Prokaryotic nitrate reduction

Characteristic	Assimilatory, NO3− assimilation	Dissimilatory
		NO3− respiration	NO3− reduction
Nitrate reductase	Assimilatory Nas	Respiratory Nar	Dissimilatory Nap
Location	Cytoplasm	Membrane	Periplasm
Reaction catalyzed	NO3−⇒NO2−	NO3−⇒NO2−	NO3−⇒NO2−
Structural genes	nasCAa/narBb	narGHI	napAB
Prosthetic groups	FADc, FeSd, MGD	cytbe, FeS, MGD	cytc, FeS, MGD
Nitrate transport	Yes	Yes	No
Function	Biosynthesis of N compounds	PMF (nitrate respiration and denitrification)	2H ⇓f and denitrification
Regulationg
O2	No	Yes	No/yes
NH4+	Yes	No	No
NO3−/NO2−	Yes	Yes	No/yes

^aFollowing the gene designation in K. oxytoca for the NADH-nitrate reductase. 

^bFollowing the gene designation in cyanobacteria for the ferredoxin-nitrate reductase. 

^cFAD is present in the diaphorase subunit of the NADH-dependent nitrate reductases, but it is absent from the cyanobacterial ferredoxin-nitrate reductase. 

^dFeS, iron-sulfur centers. 

^ecytb, cytochrome b. 

^f2H⇓, dissipation of reducing power. A PMF can be generated if a proton-translocating complex is involved in the electron transfer, but in most cases, this seems to be insufficient to support ATP synthesis coupled to nitrate reduction. 

^gSome differences in regulation in prokaryotic organisms have been reported.