Open AccessA connecting hinge represses the activity of endothelial nitric oxide synthase
Author(s) -
Mohammad Mahfuzul Haque,
Koustubh Panda,
Jesús Tejero,
Kulwant S. Aulak,
Mohammed Fadlalla,
Anthony T. Mustovich,
Dennis J. Stuehr
Publication year - 2007
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.0700332104
Subject(s) - enos , hinge , nitric oxide synthase , nitric oxide synthase type iii , nitric oxide , chemistry , endothelial nos , biochemistry , proline , atp synthase , enzyme , medicine , biology , endocrinology , amino acid , mechanical engineering , engineering
In mammals, endothelial nitric oxide synthase (eNOS) has the weakest activity, being one-tenth and one-sixth as active as the inducible NOS (iNOS) and the neuronal NOS (nNOS), respectively. The basis for this weak activity is unclear. We hypothesized that a hinge element that connects the FMN module in the reductase domain but is shorter and of unique composition in eNOS may be involved. To test this hypothesis, we generated an eNOS chimera that contained the nNOS hinge and two mutants that either eliminated (P728IeNOS) or incorporated (I958PnNOS) a proline residue unique to the eNOS hinge. Incorporating the nNOS hinge into eNOS increased NO synthesis activity 4-fold, to an activity two-thirds that of nNOS. It also decreased uncoupled NADPH oxidation, increased the apparentK m O2 for NO synthesis, and caused a faster heme reduction. Eliminating the hinge proline had similar, but lesser, effects. Our findings reveal that the hinge is an important regulator and show that differences in its composition restrict the activity of eNOS relative to other NOS enzymes.