title: Kinetics of Nitrite Reduction and Peroxynitrite Formation by Ferrous Heme in Human Cystathionine β-Synthase.
abstract: Cystathionine β-synthase (CBS) is a pyridoxal phosphate-dependent enzyme that catalyzes the condensation of homocysteine with serine or with cysteine to form cystathionine and either water or hydrogen sulfide, respectively. Human CBS possesses a noncatalytic heme cofactor with cysteine and histidine as ligands, which in its oxidized state is relatively unreactive. Ferric CBS (Fe(III)-CBS) can be reduced by strong chemical and biochemical reductants to Fe(II)-CBS, which can bind carbon monoxide (CO) or nitric oxide (NO(•)), leading to inactive enzyme. Alternatively, Fe(II)-CBS can be reoxidized by O2to Fe(III)-CBS, forming superoxide radical anion (O2 (̇̄)). In this study, we describe the kinetics of nitrite (NO2 (-)) reduction by Fe(II)-CBS to form Fe(II)NO(•)-CBS. The second order rate constant for the reaction of Fe(II)-CBS with nitrite was obtained at low dithionite concentrations. Reoxidation of Fe(II)NO(•)-CBS by O2showed complex kinetic behavior and led to peroxynitrite (ONOO(-)) formation, which was detected using the fluorescent probe, coumarin boronic acid. Thus, in addition to being a potential source of superoxide radical, CBS constitutes a previously unrecognized source of NO(•)and peroxynitrite.
authors: From the Departamento de Bioquímica, Facultad de Medicina, Center for Free Radical and Biomedical Research, and scarballal@fmed.edu.uy scarballal@gmail.com.
authors: Sebastián
authors: S
authors: Carballal
authors: Center for Free Radical and Biomedical Research, and Laboratorio de Enzimología, Facultad de Ciencias, Universidad de la República, Montevideo 11800, Uruguay and.
authors: Ernesto
authors: E
authors: Cuevasanta
authors: the Department of Biological Chemistry, Medical Center, University of Michigan, Ann Arbor, Michigan 48109-0600.
authors: Pramod K
authors: PK
authors: Yadav
authors: the Department of Biological Chemistry, Medical Center, University of Michigan, Ann Arbor, Michigan 48109-0600.
authors: Carmen
authors: C
authors: Gherasim
authors: the Department of Biological Chemistry, Medical Center, University of Michigan, Ann Arbor, Michigan 48109-0600.
authors: David P
authors: DP
authors: Ballou
authors: Center for Free Radical and Biomedical Research, and Laboratorio de Enzimología, Facultad de Ciencias, Universidad de la República, Montevideo 11800, Uruguay and.
authors: Beatriz
authors: B
authors: Alvarez
authors: the Department of Biological Chemistry, Medical Center, University of Michigan, Ann Arbor, Michigan 48109-0600 rbanerje@umich.edu.
authors: Ruma
authors: R
authors: Banerjee
mesh_terms: D002248:Carbon Monoxide / Q000378:metabolism; D003541:Cystathionine beta-Synthase / Q000737:chemistry / Q000378:metabolism*; D006418:Heme / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D009569:Nitric Oxide / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D030421:Peroxynitrous Acid / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism
chemical_list: D009573:Nitrites; D013481:Superoxides; D030421:Peroxynitrous Acid; D009569:Nitric Oxide; D006418:Heme; D002248:Carbon Monoxide; D003541:Cystathionine beta-Synthase; D010100:Oxygen
keywords: heme; hemeprotein; kinetics; nitric oxide; nitrite; oxygen; oxygen radicals; peroxynitrite; superoxide ion