Oxidative stress, reactive species and antioxidants Repair of protein radicals

J. Gebicki, Anastasia S. Domazou, Thomas Nauser, Daniel Steinmann, Willem H. Koppenol

Research output: Contribution to journalMeeting abstractpeer-review

Abstract

Hydroxyl radicals and peroxynitrous acid oxidize proteins, which
ultimately results in their denaturation. Random radical generation on
the surface of the protein without dioxygen present leads to intramolecular
electron transfer, with the last step the oxidation of tyrosine
by the tryptophanyl radical. In the presence of dioxygen aliphatic
radicals form oxidizing peroxyl radicals. Once a radical is formed,
can it be repaired, does it react with dioxygen or is it ‘‘repaired’’ by
intramolecular electron transfer?
Glutathione repairs a tryptophan radical in lysozyme with a rate
constant of (1.05 ± 0.05) × 105 M-1s-1, while ascorbate repairs
tryptophanyl and tyrosyl radicals ca. three orders of magnitude faster.
Glutathione generally reacts slowly, such that formation of peroxyl
radicals cannot be prevented. These peroxyl radicals are reduced by
glutathione to hydroperoxides, a process that cannot be characterized
as a repair. Furthermore, the resulting thiyl radical is capable of
hydrogen abstraction. Although physiologically not significant, selenoglutathione
reduces tyrosyl radicals as fast as ascorbate. The
reaction of protein radicals (insulin, b-lactoglobulin, pepsin, chymotrypsin,
and bovine serum albumin) with ascorbate is competitive
with dioxygen, leaves an innocuous ascorbyl radical, and is therefore
a true repair. The well-documented loss of ascorbate in living
organisms subjected to oxidative stress may result from repair of
protein radicals.
Original languageEnglish
Pages (from-to)S35-S36
Number of pages2
JournalAmino Acids
Volume37
Issue number1
Publication statusPublished - Jul 2009

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