title: Why do nitric oxide synthases use tetrahydrobiopterin?
abstract: We are combining stopped-flow, stop-quench, and rapid-freezing kinetic methods to help clarify the unique redox roles of tetrahydrobiopterin (H(4)B) in NO synthesis, which occurs via the consecutive oxidation of L-arginine (Arg) and N-hydroxy-L-arginine (NOHA). In the Arg reaction, H(4)B radical formation is coupled to reduction of a heme Fe(II)O(2) intermediate. The tempo of this electron transfer is important for coupling Fe(II)O(2) formation to Arg hydroxylation. Because H(4)B provides this electron faster than can the NOS reductase domain, H(4)B appears to be a kinetically preferred source of the second electron for oxygen activation during Arg hydroxylation. A conserved Trp (W457 in mouse inducible NOS) has been shown to influence product formation by controlling the kinetics of H(4)B electron transfer to the Fe(II)O(2) intermediate. This shows that the NOS protein tunes H(4)B redox function. In the NOHA reaction the role of H(4)B is more obscure. However, existing evidence suggests that H(4)B may perform consecutive electron donor and acceptor functions to reduce the Fe(II)O(2) intermediate and then ensure that NO is produced from NOHA.
authors.affiliation: Department of Immunology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH 44195, USA.
authors.forename: Chin-Chuan
authors.initials: CC
authors.lastname: Wei
authors.forename: Zhi-Qiang
authors.initials: ZQ
authors.lastname: Wang
authors.forename: Abigail L
authors.initials: AL
authors.lastname: Meade
authors.forename: John F
authors.initials: JF
authors.lastname: McDonald
authors.forename: Dennis J
authors.initials: DJ
authors.lastname: Stuehr
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001120:Arginine / Q000378:metabolism; D001708:Biopterins / Q000031:analogs & derivatives* / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D009569:Nitric Oxide / Q000096:biosynthesis; D019001:Nitric Oxide Synthase / Q000737:chemistry* / Q000378:metabolism*; D010084:Oxidation-Reduction; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D011994:Recombinant Proteins; D001708:Biopterins; D009569:Nitric Oxide; D001120:Arginine; D019001:Nitric Oxide Synthase; C003402:sapropterin