Abstract
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.
Original language | English (US) |
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Pages (from-to) | 8197-8204 |
Number of pages | 8 |
Journal | Journal of Biological Chemistry |
Volume | 281 |
Issue number | 12 |
DOIs | |
State | Published - Mar 24 2006 |
ASJC Scopus subject areas
- Biochemistry
- Molecular Biology
- Cell Biology