Photosensitization of Methyl Linoleate Oxidation by Tryptophan in Peptides

Abstract

The ability of tryptophan in peptides to photosensitize the oxidation of methyl linoleate (ML) was evaluated. Purified ML was irradiated (λ > 270 nm) alone or in the presence of a tryptophan‐containing peptide in ethanol solution. Oxidation was monitored by measuring the dienc hydroperoxides formed from ML by high performance liquid chromatography. N‐acetylphenylalanyltryptophan (NAPT) and N‐acetyltryptophan were about 2‐fold more effective as photosensitizers than leucyltryptophan and tryptophylleucine. N‐acetylphenylalanyltryptophan photolyzed in ethanol to form multiple photoproducts including N‐formylkynurenine‐type compounds. However, the NAPT photoproducts did not photosensitize the oxidation of ML and N‐formylkynurenine was about 8% as effective as NAPT. Sodium azide partially quenched the photooxidation sensitized by NAPT.

Uv‐induced Protein Alterations and Lipid Oxidation in Erythrocyte Membranes

“…This result is consistent with the absorption spectra for tryptophan or tyrosine but not that of cystine. Based on many previous studies demonstrating that photoinactivation of enzymes in solution is initiated by tryptophan (Grossweiner et al, 1976) and our previous result that tryptophan in peptides photosensitizes lipid oxidation in nonaqueous solution (Kochevar and Yoon, 1983), we conclude that tryptophan is the most likely chromophore in this study.…”

“…Photobiological changes initiated by tryptophan as the chromophore are often attributed to formation of a photooxidation product, N-formylkynurenine, which absorbs at wavelengths greater than 300 nm and sensitizes protein oxidation (Walrant and Santus, 1974a,b). However, tryptophan in peptides has been reported to directly photosensitize adjacent amino acids in polypeptide chains by an intramolecular electron transfer mechanism (Pigault and Gerard, 1989) and lipid oxidation (Kochevar and Yoon, 1983). Photosensitization by N-formylkynurenine would require more efficient protein loss in samples irradiated at 280 nm followed by irradiation at 313 nm than by 280 rim radiation alone.…”

Comparative Evaluation on Mouse Nasal Immunogenicity of Arylmethane‐, Xanthene‐, Quinone‐Imine‐, and Acridine‐Dye‐Inactivated Sendai Virus Vaccines

“…Recently, there are reports on the important role of singlet oxygen on photosensitization by miscellaneous dyes (1,2,4,7,14) and a function of NaN3 as an antioxidant in photooxidation (5,9,14). On the basis of the data, NaN3 of a disinfectant in this experiment might have acted as a singlet oxygen scavenger in the virus-dye mixtures, in contrast with so-called sensitized photochemical reactions involving oxygen.…”