title: Stereospecificity of horseradish peroxidase.
abstract: We report here on the stereospecificity observed in the action of horseradish peroxidase (HRPC) on monophenol and diphenol substrates. Several enantiomers of monophenols and o-diphenols were assayed: L-tyrosinol, D-tyrosinol, L-tyrosine, DL-tyrosine, D-tyrosine, L-dopa, DL-dopa, D-dopa, L-alpha-methyldopa, DL-alpha-methyldopa, DL-adrenaline, D-adrenaline, L-isoproterenol, DL-isoproterenol and D-isoproterenol. The electronic density at the carbon atoms in the C-1 and C-2 positions of the benzene ring were determined by NMR assays (delta1 and delta2). This value is related to the nucleophilic power of the oxygen atom of the hydroxyl groups and to its oxidation-reduction capacity. The spatial orientation of the ring substituents resulted in lower Km values for L- than for D-isomers. The kcat values for substrates capable of saturating the enzyme were lower for D- than for L-isomers, although both have the same delta1 and delta2 NMR values for carbons C-1 and C-2, and therefore the same oxidation-reduction potential. In the case of substrates that cannot saturate the enzyme, the values of the binding constant for compound II (an intermediate in the catalytic cycle) followed the order: L-isomer>DL-isomer>D-isomer. Therefore, horseradish peroxidase showed stereospecificity in its affinity toward its substrates (K m) and in their transformation reaction rates (k cat).
authors.affiliation: Grupo de Investigación de Enzimología, Departamento de Bioquímica y Biología Molecular-A, Facultad de Biología, Universidad de Murcia, A. Correos 4021, E-30080, Murcia, Spain.
authors.forename: M Angeles
authors.initials: MA
authors.lastname: Gilabert
authors.forename: Lorena G
authors.initials: LG
authors.lastname: Fenoll
authors.forename: Francisco
authors.initials: F
authors.lastname: García-Molina
authors.forename: Pedro A
authors.initials: PA
authors.lastname: García-Ruiz
authors.forename: José
authors.initials: J
authors.lastname: Tudela
authors.forename: Francisco
authors.initials: F
authors.lastname: García-Cánovas
authors.forename: José N
authors.initials: JN
authors.lastname: Rodríguez-López
mesh_terms: D000465:Algorithms; D015306:Biogenic Monoamines / Q000737:chemistry / Q000378:metabolism; D006735:Horseradish Peroxidase / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007545:Isoproterenol / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D010636:Phenols / Q000737:chemistry / Q000378:metabolism; D013237:Stereoisomerism; D013379:Substrate Specificity; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism
chemical_list: D015306:Biogenic Monoamines; D010636:Phenols; D014443:Tyrosine; C039069:tyrosinol; D006735:Horseradish Peroxidase; D007545:Isoproterenol