title: Inactivation of cystathionine beta-synthase with peroxynitrite.
abstract: Cystathionine beta-synthase (CBS) is a homocysteine metabolizing enzyme that contains pyridoxal phosphate (PLP) and a six-coordinate heme cofactor of unknown function. CBS was inactivated by peroxynitrite, the product of nitric oxide and superoxide radicals. The IC(50) was approximately 150microM for 5microM ferric CBS. Stopped-flow kinetics and competition experiments showed a direct reaction with a second-order rate constant of (2.4-5.0)x10(4)M(-1)s(-1) (pH 7.4, 37 degrees C). The radicals derived from peroxynitrite, nitrogen dioxide and carbonate radical, also inactivated CBS. Exposure to peroxynitrite did not modify bound PLP but led to nitration of Trp208, Trp43 and Tyr223 and alterations in the heme environment including loss of thiolate coordination, conversion to high-spin and bleaching, with no detectable formation of oxo-ferryl compounds nor promotion of one-electron processes. This study demonstrates the susceptibility of CBS to reactive oxygen/nitrogen species, with potential relevance to hyperhomocysteinemia, a risk factor for cardiovascular diseases.
authors.affiliation: Laboratorio de Enzimología, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay.
authors.forename: Laura
authors.initials: L
authors.lastname: Celano
authors.forename: Magdalena
authors.initials: M
authors.lastname: Gil
authors.forename: Sebastián
authors.initials: S
authors.lastname: Carballal
authors.forename: Rosario
authors.initials: R
authors.lastname: Durán
authors.forename: Ana
authors.initials: A
authors.lastname: Denicola
authors.forename: Ruma
authors.initials: R
authors.lastname: Banerjee
authors.forename: Beatriz
authors.initials: B
authors.lastname: Alvarez
mesh_terms: D002245:Carbon Dioxide / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D003541:Cystathionine beta-Synthase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D004789:Enzyme Activation / Q000187:drug effects; D017353:Gene Deletion; D006418:Heme / Q000032:analysis / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008353:Mannitol / Q000494:pharmacology; D013058:Mass Spectrometry; D017942:Nitric Acid / Q000378:metabolism; D030421:Peroxynitrous Acid / Q000378:metabolism / Q000494:pharmacology*; D010648:Phenylacetates / Q000494:pharmacology; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D013056:Spectrophotometry, Ultraviolet; D013438:Sulfhydryl Compounds / Q000378:metabolism
chemical_list: D010648:Phenylacetates; D013438:Sulfhydryl Compounds; D002245:Carbon Dioxide; D030421:Peroxynitrous Acid; C008070:4-hydroxyphenylacetic acid; D008353:Mannitol; D017942:Nitric Acid; D006418:Heme; D003541:Cystathionine beta-Synthase