Biomaterial Database

pH dependence of the reoxidation of p-hydroxybenzoate hydroxylase 2,4-dihydroxybenzoate complex. 1984

A Wessiak, and L M Schopfer, and V Massey

Oxidation of reduced p-OH-benzoate hydroxylase . 2,4-diOH-benzoate complex by molecular oxygen occurs in four clearly defined steps. Inclusion of azide in the reaction medium slows the rate for each step. We have found that the rates for the last three steps as well as the UV/visible absorbance spectrum for the second intermediate are markedly dependent on pH. Formation of intermediate II is base-catalyzed while its decay to intermediate III is acid-catalyzed. Formation of oxidized enzyme from intermediate III is base-catalyzed. The spectrum of intermediate II is shifted to longer wavelengths on raising the pH. A pKa of about 7.8 can be calculated for each of these pH-dependent transitions, except for the rate of formation of oxidized enzyme. This rate appears to be directly dependent on hydroxide ion concentration. The presence of azide does not change the observed pH dependence. These results are discussed in the context of a 4a,5-ring opened flavin structure for intermediate II.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D010084	Oxidation-Reduction	A chemical reaction in which an electron is transferred from one molecule to another. The electron-donating molecule is the reducing agent or reductant; the electron-accepting molecule is the oxidizing agent or oxidant. Reducing and oxidizing agents function as conjugate reductant-oxidant pairs or redox pairs (Lehninger, Principles of Biochemistry, 1982, p471).	Redox,Oxidation Reduction
D011485	Protein Binding	The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments.	Plasma Protein Binding Capacity,Binding, Protein
D002621	Chemistry	A basic science concerned with the composition, structure, and properties of matter; and the reactions that occur between substances and the associated energy exchange.
D006863	Hydrogen-Ion Concentration	The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH	pH,Concentration, Hydrogen-Ion,Concentrations, Hydrogen-Ion,Hydrogen Ion Concentration,Hydrogen-Ion Concentrations
D006899	Mixed Function Oxygenases	Widely distributed enzymes that carry out oxidation-reduction reactions in which one atom of the oxygen molecule is incorporated into the organic substrate; the other oxygen atom is reduced and combined with hydrogen ions to form water. They are also known as monooxygenases or hydroxylases. These reactions require two substrates as reductants for each of the two oxygen atoms. There are different classes of monooxygenases depending on the type of hydrogen-providing cosubstrate (COENZYMES) required in the mixed-function oxidation.	Hydroxylase,Hydroxylases,Mixed Function Oxidase,Mixed Function Oxygenase,Monooxygenase,Monooxygenases,Mixed Function Oxidases,Function Oxidase, Mixed,Function Oxygenase, Mixed,Oxidase, Mixed Function,Oxidases, Mixed Function,Oxygenase, Mixed Function,Oxygenases, Mixed Function
D013053	Spectrophotometry	The art or process of comparing photometrically the relative intensities of the light in different parts of the spectrum.
D015109	4-Hydroxybenzoate-3-Monooxygenase	A flavoprotein that catalyzes the synthesis of protocatechuic acid from 4-hydroxybenzoate in the presence of molecular oxygen. EC 1.14.13.2.	p-Hydroxybenzoate Hydroxylase,para-Hydroxybenzoate Hydroxylase,4 Hydroxybenzoate 3 Monooxygenase,Hydroxylase, p-Hydroxybenzoate,Hydroxylase, para-Hydroxybenzoate,p Hydroxybenzoate Hydroxylase,para Hydroxybenzoate Hydroxylase
D055598	Chemical Phenomena	The composition, structure, conformation, and properties of atoms and molecules, and their reaction and interaction processes.	Chemical Concepts,Chemical Processes,Physical Chemistry Concepts,Physical Chemistry Processes,Physicochemical Concepts,Physicochemical Phenomena,Physicochemical Processes,Chemical Phenomenon,Chemical Process,Physical Chemistry Phenomena,Physical Chemistry Process,Physicochemical Phenomenon,Physicochemical Process,Chemical Concept,Chemistry Process, Physical,Chemistry Processes, Physical,Concept, Chemical,Concept, Physical Chemistry,Concept, Physicochemical,Concepts, Chemical,Concepts, Physical Chemistry,Concepts, Physicochemical,Phenomena, Chemical,Phenomena, Physical Chemistry,Phenomena, Physicochemical,Phenomenon, Chemical,Phenomenon, Physicochemical,Physical Chemistry Concept,Physicochemical Concept,Process, Chemical,Process, Physical Chemistry,Process, Physicochemical,Processes, Chemical,Processes, Physical Chemistry,Processes, Physicochemical
D062385	Hydroxybenzoates	Benzoate derivatives substituted by one or more hydroxy groups in any position on the benzene ring.	Hydroxybenzoic Acids,Acids, Hydroxybenzoic