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 t...
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Published in | The Journal of biological chemistry Vol. 281; no. 12; pp. 8197 - 8204 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
United States
Elsevier Inc
24.03.2006
American Society for Biochemistry and Molecular Biology |
Subjects | |
Online Access | Get full text |
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Summary: | 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 ∼300 min. It is followed by a faster autoreduction reaction of the heme iron with a lifetime of ∼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. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0021-9258 1083-351X |
DOI: | 10.1074/jbc.M507328200 |