Biomaterial Database

Mechanism of enzymatic and non-enzymatic tyrosine iodination. Inhibition by excess hydrogen peroxide and/or iodide. 1985

M Huwiler, and U Bürgi, and H Kohler

Non-enzymatic (I2-mediated) and lactoperoxidase-catalyzed iodination of tyrosine are inhibited by excess iodide (I-) and/or hydrogen peroxide (H2O2). This phenomenon is a consequence of the concentration-dependent dual role of I- and H2O2 in the iodinating system. I- and H2O2, in addition to their function as primary substrates of peroxidase, may act as alternative 'iodine acceptors' and therefore compete with tyrosine for the active iodinating agent, irrespective of whether this compound is an enzyme-associated iodinium cation (E X I delta +) or an equivalent oxidized iodine species (IOH, IC1, I2). The competitive reaction pathways resulting from excess I- and/or H2O2 in the iodination system are I2/I-3 generation and/or pseudo-catalatic degradation of H2O2, respectively. Our results also demonstrate that I2 (and alternative medium-dependent oxidized iodine species such as IOH and IC1) generated in the iodination system may play an important role as iodinating agent(s). They serve as a substitute for the enzyme-bound iodinium species (E X I delta +), if the prevailing I- concentration favours this pathway. The proposed mechanism of the various antagonistic and interactive reaction pathways is summarized in a scheme.

UI	MeSH Term	Description	Entries
D007454	Iodides	Inorganic binary compounds of iodine or the I- ion.	Iodide
D007455	Iodine	A nonmetallic element of the halogen group that is represented by the atomic symbol I, atomic number 53, and atomic weight of 126.90. It is a nutritionally essential element, especially important in thyroid hormone synthesis. In solution, it has anti-infective properties and is used topically.	Iodine-127,Iodine 127
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D007784	Lactoperoxidase	An enzyme derived from cow's milk. It catalyzes the radioiodination of tyrosine and its derivatives and of peptides containing tyrosine.
D008956	Models, Chemical	Theoretical representations that simulate the behavior or activity of chemical processes or phenomena; includes the use of mathematical equations, computers, and other electronic equipment.	Chemical Models,Chemical Model,Model, Chemical
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
D010544	Peroxidases		Ovoperoxidase
D002384	Catalysis	The facilitation of a chemical reaction by material (catalyst) that is not consumed by the reaction.	Catalyses
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.
D006861	Hydrogen Peroxide	A strong oxidizing agent used in aqueous solution as a ripening agent, bleach, and topical anti-infective. It is relatively unstable and solutions deteriorate over time unless stabilized by the addition of acetanilide or similar organic materials.	Hydrogen Peroxide (H2O2),Hydroperoxide,Oxydol,Perhydrol,Superoxol,Peroxide, Hydrogen