Dopaquinone redox exchange with dihydroxyindole and dihydroxyindole carboxylic acid
Edge, R, d'Ischia, M, Land, EJ, Navaratnam, S, Panzella, L, Pezzella, A, Ramsden, CA and Riley, PA 2006, 'Dopaquinone redox exchange with dihydroxyindole and dihydroxyindole carboxylic acid' , Pigment Cell Research, 19 (5) , pp. 443-450.Full text not available from this repository.
A pulse radiolytic investigation has been conducted to establish whether a redox reaction takes place between dopaquinone and 5,6-dihydroxyindole (DHI) and its 2-carboxylic acid (DHICA) and to measure the rate constants of the interactions. To obviate possible confounding reactions, such as nucleophilic addition, the method employed to generate dopaquinone used the dibromide radical anion acting on dopa to form the semiquinone which rapidly disproportionates to dopaquinone. In the presence of DHI the corresponding indole-5,6-quinone (and/or tautomers) was also formed directly but, by judicious selection of suitable relative concentrations of initial reactants, we were able to detect the formation of additional indolequinone from the redox exchange reaction of DHI with dopaquinone which exhibited a linear dependency on the concentration of DHI. Computer simulation of the experimental time profiles of the absorption changes showed that, under the conditions chosen, redox exchange does proceed but not quite to completion, a forward rate constant of 1.4 x 10(6)/M/s being obtained. This is in the same range as the rate constants previously established for reactions of dopaquinone with cyclodopa and cysteinyldopa. In similar experiments carried out with DHICA, the reaction more obviously does not go to completion and is much slower, k (forward) =1.6 x 10(5)/M/s. We conclude that, in the eumelanogenic pathway, DHI oxidation may take place by redox exchange with dopaquinone, although such a reaction is likely to be less efficient for DHICA.
|Uncontrolled Keywords:||Dopaquinone, dihydroxyindole, dihydroxyindole carboxylic acid, redox exchange, pulse radiolysis|
|Themes:||Subjects / Themes > Q Science > Q Science (General)|
Subjects outside of the University Themes
|Schools:||Colleges and Schools > College of Science & Technology|
Colleges and Schools > College of Science & Technology > School of Environment and Life Sciences
|Journal or Publication Title:||Pigment Cell Research|
|Depositing User:||H Kenna|
|Date Deposited:||08 Aug 2007 10:29|
|Last Modified:||27 Sep 2011 12:19|
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