HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hewson, W. D. Articles by Dunford, H. B. Search for Related Content PubMed PubMed Citation Articles by Hewson, W. D. Articles by Dunford, H. B. Social Bookmarking                      What's this?

JBC, Vol. 251, Issue 19, 6043-6052, Oct, 1976

Stoichiometry of the reaction between horseradish peroxidase and p-cresol

W. D. Hewson and H. B. Dunford

Over a wide range of pH horseradish peroxidase compound I can be reduced quantitatively via compound II to the native enzyme by only 1 molar equivalent of p-cresol. Since 2 molar equivalents of electrons are required for the single turnover of the enzymatic cycle, p-cresol behaves as a 2-electron reductant. With p-cresol and compound I in a 1:1 ratio compound II and p-methylphenoxy radicals are obtained in the transient state. Compound II is then reduced to the native enzyme. A possible explanation for the facile reduction of compound II involves reaction with the dimerization product of these radicals, 1/2 molar equivalent of 2,2'-dihydroxy-5,5'-dimethylbiphenyl. If only 1/2 molar equivalent of p-cresol is present, than at high pH the reduction stops at compound II. The major steady state peroxidase oxidation product of p-cresol (with p-cresol in large excess compared to the enzyme concentration) is Pummerer's ketone. Pummerer's ketone is only reactive at pH values greater than about 9 where significant amounts of the enol can be formed via the enolate anion. Therefore, in alkaline solution it is reactive with compound I, but not with compound II, which is converted into an unreactive basic form. These results indicate that Pummerer's ketone cannot be the intermediate free radical product responsible for reducing compound II in the single turnover experiments. It is postulated that Pummerer's ketone is formed only in the steady state by the reaction of the p-methylphenoxy radical with excess p-cresol.
CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				Q. Guo, C. D. Detweiler, and R. P. Mason Protein Radical Formation during Lactoperoxidase-mediated Oxidation of the Suicide Substrate Glutathione: IMMUNOCHEMICAL DETECTION OF A LACTOPEROXIDASE RADICAL-DERIVED 5,5-DIMETHYL-1-PYRROLINE N-OXIDE NITRONE ADDUCT J. Biol. Chem., March 26, 2004; 279(13): 13272 - 13283. [Abstract] [Full Text] [PDF]