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Comparative mechanisms and rates of free radical scavenging by carotenoid antioxidants
Author(s) -
Mortensen Alan,
Skibsted Leif H.,
Sampson Julia,
Rice-Evans Catherine,
Everett Steven A.
Publication year - 1997
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(97)01355-0
Subject(s) - carotenoid , scavenging , chemistry , biochemistry , antioxidant , food science
The comparative mechanisms and relative rates of nitrogen dioxide (NO 2 ⋅ ), thiyl (RS ⋅ ) and sulphonyl (RSO 2 ⋅ ) radical scavenging by the carotenoid antioxidants lycopene, lutein, zeaxanthin, astaxanthin and canthaxanthin have been determined by pulse radiolysis. All the carotenoids under study react with the NO 2 ⋅ radical via electron transfer to generate the carotenoid radical cation (Car ⋅+ ). In marked contrast the glutathione and 2‐mercaptoethanol thiyl radicals react via a radical addition process to generate carotenoid‐thiyl radical adducts [RS‐Car] ⋅ . The RSO 2 ⋅ radical undergoes both radical addition, [RSO 2 ‐Car] ⋅ and electron abstraction, Car ⋅+ . Both carotenoid adduct radicals and radical cations decay bimolecularly. Absolute rate constants for radical scavenging were in the order of ∼10 7 –10 9 M −1 s −1 and follow the sequence HO(CH 2 ) 2 S ⋅ >RSO 2 ⋅ >GS ⋅ >NO 2 ⋅ . Although there were some discernible trends in carotenoid reactivity for individual radicals, rate constants varied by no greater than a factor of 2.5. The mechanism and rate of scavenging is strongly dependent on the nature of the oxidising radical species but much less dependent on the carotenoid structure.