Regulation of the monomer-dimer equilibrium in inducible nitric-oxide synthase by nitric oxide.
The oxygenase domain of inducible nitric-oxide synthase exists as a functional tight homodimer in the presence of the substrate L-arginine and the cofactor tetrahydrobiopterin (H4B). In the absence of H4B, the enzyme is a mixture of monomer and loose dimer. We show that exposure of H4B-free enzyme to NO induces dissociation of the loose dimer into monomers in a reaction that follows single exponential decay kinetics with a lifetime of approximately 300 min. It is followed by a faster autoreduction reaction of the heme iron with a lifetime of approximately 30 min and the concurrent breakage of the proximal iron-thiolate bond, forming a five-coordinate NO-bound ferrous species. Mass spectrometry revealed that the NO-induced monomerization is associated with intramolecular disulfide bond formation between Cys104 and Cys109, located in the zinc-binding motif. The regulatory effect of NO as a dimer inhibitor is discussed in the context of the structure/function relationships of this enzyme.
Li
David
D
Department of Physiology and Biophysics, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461, USA.
Hayden
Eric Y
EY
Panda
Koustubh
K
Stuehr
Dennis J
DJ
Deng
Haiteng
H
Rousseau
Denis L
DL
Yeh
Syun-Ru
SR
D020816:Amino Acid Motifs; D000818:Animals; D001120:Arginine / Q000737:chemistry*; D001708:Biopterins / Q000031:analogs & derivatives* / Q000737:chemistry; D002614:Chelating Agents / Q000494:pharmacology; D002845:Chromatography; D003545:Cysteine / Q000737:chemistry; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry; D004926:Escherichia coli / Q000378:metabolism; D006418:Heme / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D013058:Mass Spectrometry; D051379:Mice; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D009569:Nitric Oxide / Q000737:chemistry / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman; D013329:Structure-Activity Relationship; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013997:Time Factors; D014508:Urea / Q000494:pharmacology; D015032:Zinc / Q000737:chemistry
D002614:Chelating Agents; D004220:Disulfides; D013438:Sulfhydryl Compounds; D001708:Biopterins; D009569:Nitric Oxide; D006418:Heme; D014508:Urea; D001120:Arginine; D007501:Iron; D052247:Nitric Oxide Synthase Type II; C003402:sapropterin; D015032:Zinc; D003545:Cysteine