REACTIVE OXYGEN SPECIES - Oxidation of Amino Acids, Peptides, and Proteins: Kinetics and Mechanism - page 151

TABLE 4.9. Hydroperoxides of Amino Acids, Peptides, and Proteins Employed to
React with Prx's

Relative
concentration of
Hydroperoxide
(mmol per mol of
Treated compound)

Treatment to
Produce
Hydroperoxide

Reduced form
of Prx's
Remaining (%) Hydroperoxide

Leu γ-Irradiation 24 16 ± 1

N -Acetyl Leu γ-Irradiation 8 0

N -Acetyl Leu amide γ-Irradiation 25 0

N -Acetyl Leu methyl
ester

γ-Irradiation 23 0

Ile 25 0

γ-Irradiation

N -Acetyl Ile γ-Irradiation 11 0

N -Acetyl Ile amide γ-Irradiation 11 0

gly-Leu γ-Irradiation 22 0

Leu-gly γ-Irradiation 39 0

gly-Leu-Leu-gly γ-Irradiation 20 0

Tyr Photolysis 62 19 ± 25

gly-Tyr-gly Photolysis 196

33 ± 28

His Photolysis 16 27 ± 8

Lysozyme Photolysis 45 55 ± 8

BSA γ-Irradiation 759 30 ± 1

BSA Photolysis 583 -

The level of the reduced form of Prx's remaining was determined after incubation for 10-30
seconds with typically 5 µM Prx2 or Prx3 and 7 µM hydroperoxide and is shown as means ± SD
( n = 2-5) for pooled Prx2 and Prx3.
Adapted from Peskin et al. [198] with the permission of the Biochemical Society.

protein were efficient inhibitors of tryptic and chymotryptic activities of 26S
proteasome. Loss of actcitivity may be related to the reaction with thiols in
the proteasome. The inhibition of the proteasome activity by oxidized proteins
may have implications in cell signaling processes because of the effect on the
turnover of native proteins [189]. More recently, selenomethionine (SeMet)
was shown to scavenge hydroperoxides present on amino acids, peptides, and
proteins [202]. Significantly, Met could not remove these peroxides. The reac-
tion of SeMet with peroxides resulted in selenoxide, confirmed by HPLc
technique. In the presence of gSH, thioredoxin reductase (TrxR), thioredoxin
(Trx), and NADPH system, selenoxide could be converted back to SeMet. The
scheme of this recycling having removal of peroxides is presented in Figure
4.13 [202]. Reactions of selenoxide with gSH, TrxR/NADPH, and TrxR/Tx/
NADPH were rapid, indicating enhanced removal rate of peroxide. A loss of
peroxide was stoichiometric in consuming NADPH in the TrxR/Trx/NADPH
system. This suggests efficient removal of peroxides. SeMet as an effective