REACTIVE OXYGEN SPECIES - Oxidation of Amino Acids, Peptides, and Proteins: Kinetics and Mechanism - page 149

Beta-carotene
0.9%

GSH
0.4%

DNA
5.5%

Ascorbate
16.5%

Tocopherols
0.5%

RNA
6.9%

NAD+/NADH
0.3%

NADP+/NADPH
0.3%

Cholesterol
0.0%

Lipids
0.2%

Protein
68.5%

Figure 4.12. Predicted consumption of 1 O 2 by intracellular targets calculated using the
rate constant data given in Reference 151 and the average concentration of each com-
ponent within a typical leukocyte cell [186] (adapted from Davies [130] with the per-
mission of Elsevier Inc.). See color insert.

The hydroperoxides of peptides and proteins have been analyzed to dem-
onstrate their production within proteins [133, 188, 189]. A wide range of
sensitizers formed peroxides and the overlal yield was enhanced in using D 2 O
as a solvent. This is consistent with that 1 O 2 was involved in forming peroxides.
Research on the nature and exact position of these peroxides within the
protein structure are in progress. Basically, interest in hydroperoxides is related
to their high oxidation ability to induce damage by either directly inhibiting
thiol-dependent proteins, cathepsins, and sarcoplasmic/endoplasmic reticulum
ca 2+ -ATPase or by producing additional radical species in the presence of
trace amounts of a transition metal ion [13, 130, 189-194]. Examples include
the modification of DNA by protein hydroperoxides and the formation of
DNA-protein cross-links [195, 196] and the decomposition of the hydroper-
oxides of Trp, His, and Try residues and a number of proteins at room tem-
perature and in the presence of Fe 2+ EDTA and NaBH 4 [133, 179, 188, 197].
The reactivity of hydroperoxides of amino acid, peptide, and protein
hydroperoxides with peroxiredoxin s (Prx's) 2 and 3 has been conducted to
quantitatively assess the importance of these reactions and also to know if
reactions have significant rates to be involved in detoxification mechanism
[198]. The second-order rate constants are presented in Table 4.8. Prx reacted
faster than that of Prx2 and the rate constants varied from 2 × 10 3 for histidine