Antioxidant reactions of dihydrolipoic acid and lipoamide with triplet duroquinone.
The oxidation of the antioxidants dihydrolipoate and lipoamide by triplet duroquinone (3DQ) has been studied by laser flash photolysis and time-resolved resonance Raman (TR3) spectroscopy. Reaction of 3DQ with lipoamide by electron transfer [k(H2O)/k(D2O approximately 1] was more rapid than with dihydrolipoate, in which a proton is also involved [k(H2O)/k(D2O approximately 2]. For dihydrolipoate at neutral pH the undeprotonated form was the major reactive species with k approximately 10(9) dm3 mol-1 s-1. At higher pH values the reaction of ionised (thiolate) forms was observed with k > or = 4 x 10(9) dm3 mol-1 s-1. The electron transfer mechanism of reaction between 3DQ and lipoamide was confirmed by TR3 spectra in which formation of the durosemiquinone radical anion and lipoamide disulfide radical cation (RSS+.) was observed.
Bisby
R H
RH
Department of Biological Sciences, University of Salford, United Kingdom.
Parker
A W
AW
D000975:Antioxidants / Q000378:metabolism*; D016227:Benzoquinones / Q000378:metabolism*; D005609:Free Radicals / Q000378:metabolism; D007700:Kinetics; D007834:Lasers; D010782:Photolysis; D013059:Spectrum Analysis, Raman; D008063:Thioctic Acid / Q000031:analogs & derivatives* / Q000378:metabolism
D000975:Antioxidants; D016227:Benzoquinones; D005609:Free Radicals; D008063:Thioctic Acid; C015144:dihydrolipoic acid; C013091:lipoamide; C034257:duroquinone