Nitrite controls the release of nitric oxide in Pseudomonas aeruginosa cd1 nitrite reductase.
Nitrite reductase (cd1NIR) from Pseudomonas aeruginosa, which catalyses the reduction of nitrite to nitric oxide (NO), contains a c-heme as the electron acceptor and a d1-heme where catalysis occurs. Reduction involves binding of nitrite to the reduced d1-heme, followed by dehydration to yield NO; release of NO and re-reduction of the enzyme close the cycle. Since NO is a powerful inhibitor of ferrous hemeproteins, enzymatic turnover demands the release of NO. We recently discovered that NO dissociation from the ferrous d1-heme is fast, showing that cd1NIR behaves differently from other hemeproteins. Here we demonstrate for the first time that the physiological substrate nitrite displaces NO from the ferrous enzyme, which enters a new catalytic cycle; this reaction depends on the conserved His369 whose role in substrate stabilization is crucial for catalysis. Thus we suggest that also in vivo the activity of cd1NIR is controlled by nitrite.
Rinaldo
Serena
S
Dipartimento di Scienze Biochimiche A. Rossi Fanelli, Sapienza-Università di Roma, P.le A. Moro, 5 00185 Rome, Italy.
Brunori
Maurizio
M
Cutruzzolà
Francesca
F
D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002384:Catalysis / Q000187:drug effects; D020134:Catalytic Domain / Q000235:genetics; D003486:Cyanides / Q000737:chemistry / Q000494:pharmacology; D006418:Heme / Q000737:chemistry / Q000378:metabolism; D006639:Histidine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D016296:Mutagenesis; D009569:Nitric Oxide / Q000378:metabolism*; D009572:Nitrite Reductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D011550:Pseudomonas aeruginosa / Q000201:enzymology* / Q000235:genetics; D013379:Substrate Specificity
D001426:Bacterial Proteins; D003486:Cyanides; D009573:Nitrites; D009569:Nitric Oxide; D006418:Heme; D006639:Histidine; D009572:Nitrite Reductases