Kinetics of tyrosyl radical reduction by selenocysteine.
The rate constant for the reduction of the tyrosyl radical with selenocysteine has been measured to investigate whether selenocysteine is capable of repair of protein radicals. Tyrosyl radicals, both free in solution and in insulin, were generated by means of pulse radiolysis and laser flash photolysis in aqueous solution. The rate constant for the reaction of free N-acetyl-tyrosyl-amine radicals with selenocysteine is (8 +/- 2) x 10 (8) M (-1) s (-1), and that for tyrosyl radicals in insulin is (1.6 +/- 0.4) x 10 (8) M (-1) s (-1). The rate constant for the reaction of selenoglutathione with the N-acetyl-tyrosyl-amine radical is (5 +/- 2) x 10 (8) M (-1) s (-1). In contrast, cysteine and glutathione react more slowly than their selenium analogues with the tyrosyl radical: the reactions of N-acetyl-tyrosyl-amine radicals with cysteine and glutathione are 3 and 5 orders of magnitude slower, respectively, than those with selenocysteine and selenoglutathione, while those of tyrosyl radicals in insulin are 3 and 2 orders of magnitude slower, respectively.
Steinmann
Daniel
D
Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland.
Nauser
Thomas
T
Beld
Joris
J
Tanner
Martin
M
Günther
Detlef
D
Bounds
Patricia L
PL
Koppenol
Willem H
WH
D005609:Free Radicals / Q000737:chemistry*; D010782:Photolysis; D011675:Pulse Radiolysis / Q000379:methods; D017279:Selenocysteine / Q000737:chemistry*; D014443:Tyrosine / Q000737:chemistry*
D005609:Free Radicals; D017279:Selenocysteine; D014443:Tyrosine