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EC Number
General Information
Commentary
Reference
physiological function
the Nap-deficient mutant KD102 shows increased diauxic lag when switched from aerobic to anoxic respiration, suggesting Nap is responsible for shorter lags and helps in adaptation to anoxic metabolism after transition from aerobic conditions
physiological function
napAB expression is required for anaerobic growth recovery by DELTAnarXL (a deletion encompassing the bulk of narXL)
evolution
periplasmic nitrate reductase (Nap) from Desulfovibrio desulfuricans and formate dehydrogenase (Fdh) from Escherichia coli K-12, both belonging to the DMSO reductase family, subfamily I, have a very similar structure, but very different activities. The show key differences that tune them for completely different functions in living cells. Both enzymes share almost identical three-dimensional protein foldings and active sites, in terms of coordination number, geometry and nature of the ligands. The substrates of both enzymes (nitrate and formate) are polyatomic anions that also share similar charge and stereochemistry. In terms of the catalytic mechanism, both enzymes have a common activation mechanism (the sulfur-shift mechanism) that ensures a constant coordination number around the metal ion during the catalytic cycle. In spite of these similarities, they catalyze very different reactions: Nap abstracts an oxygen atom from nitrate releasing nitrite, whereas FdH catalyzes a hydrogen atom transfer from formate and releases carbon dioxide. Detailed comparison, overview. A key difference between the catalytic mechanisms of Nap and FdH is the fact that only Mo is used to reduce nitrate but in Fdhs both Mo and W are catalytically competent to oxidize formate to carbon dioxide
malfunction
a gene nap deletion mutant can no longer grow on methanol in contrast to the wild-type and shows almost abolished N2O production from nitrate
metabolism
cytochromes c encoded by genes in close proximity to the genes for XoxF proteins and methylamine dehydrogenase functions are likely involved in the metabolism with Nap, pathway overview
more
the enzyme shows a sulfur-shift mechanism catalytic mechanism, the active site is deeply buried and centered on the Mo atom, which is hexacoordinated to four sulfur atoms of two pyranopterin guanosine dinucleotides, one inorganic sulfur, and one S (Nap) atom from the side chain of a Cys, structure, structure overview. Above the region of the metal center, the enzyme presents an arginine residue, Arg354,that is proposed to be key for stabilization and substrate binding. The side chain of this residues probably interacts electrostatically with the substrates, compensating for the negative charge and favoring their interaction with the negatively charged active site
physiological function
the single subunit nitrate reductase (Nap) appears to be involved in both the assimilatory and the dissimilatory denitrification pathways. The role in the former is supported by the methanol growth deficiency of the mutant when nitrate is used as a nitrogen source, and the role in the latter is supported by the lack of accumulation of N2O in the mutant
evolution
the enzyme belongs to the DMSO reductase family
evolution
the prokaryotic nitrate reductases can be subgrouped as respiratory nitrate reductases (Nar), assimilatory nitrate reductases (Nas), and periplasmic nitrate reductases (Nap). Periplasmic nitrate reductase (Nap) and formate dehydrogenase (Fdh), both belonging to the DMSO reductase family, subfamily I, have a very similar structure, but very different activities. The show key differences that tune them for completely different functions in living cells. Both enzymes share almost identical three-dimensional protein foldings and active sites, in terms of coordination number, geometry and nature of the ligands. The substrates of both enzymes (nitrate and formate) are polyatomic anions that also share similar charge and stereochemistry. In terms of the catalytic mechanism, both enzymes have a common activation mechanism (the sulfur-shift mechanism) that ensures a constant coordination number around the metal ion during the catalytic cycle. In spite of these similarities, they catalyze very different reactions: Nap abstracts an oxygen atom from nitrate releasing nitrite, whereas FdH catalyzes a hydrogen atom transfer from formate and releases carbon dioxide. Detailed comparison, overview. A key difference between the catalytic mechanisms of Nap and FdH is the fact that only Mo is used to reduce nitrate but in Fdhs both Mo and W are catalytically competent to oxidize formate to carbon dioxide
evolution
the prokaryotic nitrate reductases can be subgrouped as respiratory nitrate reductases (Nar), assimilatory nitrate reductases (Nas), and periplasmic nitrate reductases (Nap). Periplasmic nitrate reductase (Nap) belongs to the DMSO reductase family, subfamily I
Results 1 - 10 of 26 > >>