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Reactivity of singlet oxygen toward large peptides
1Department of Physical Chemistry, Hebrew University of Jerusalem, Israel.
Photochemistry and Photobiology
|March 1, 1995
Summary
Singlet oxygen reacts less efficiently with native peptides like melittin and insulin compared to their individual amino acids. Denatured peptides, however, show reactivity similar to free amino acids.
Area of Science:
- Biochemistry
- Chemical Kinetics
Background:
- Singlet oxygen (1O2) reactions with amino acids are well-documented.
- Only five specific amino acid residues readily interact with 1O2.
Purpose of the Study:
- To investigate the reactions of 1O2 with large peptides (melittin, NPY, insulin) in native and denatured states.
- To compare peptide reactivity with constituent amino acid mixtures.
Main Methods:
- Studied singlet oxygen quenching rates.
- Compared peptide reaction rates with those of their constituent amino acid mixtures.
- Utilized native, oxidized, and fully denatured (6 M urea) peptide forms.
Main Results:
- Native peptides showed lower 1O2 quenching rates than their amino acid mixtures (ratios: NPY 0.75, melittin 0.83/0.70, insulin 0.55).
- Oxidized insulin (opened disulfide bridges) showed increased reactivity (0.80).
- Fully denatured peptides exhibited quenching rates equal to their amino acid mixtures.
Conclusions:
- Native peptide structure shields reactive amino acid residues from 1O2.
- Temporary folding or incipient secondary structures likely cause this shielding.
- Denaturation exposes residues, restoring reactivity to levels seen in free amino acids.
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