Low-molecular Peptide Model of Protein Denaturation by UVA Irradiation and the Effect of Antioxidants

Takao Ashikaga1,3, Akira Motoyama2, Hideyuki Ichikawa1, Hiroshi Itagaki 3 and Yoshihisa Sato1
1Institute For Advanced Skin Research Inc.,
2Shiseido Pharmaceutical Research Center,
3Shiseido Life science Research Center, Yokohama, Japan

Correspondence: Takao Ashikaga
Shiseido Life Science Research Center, 2-12-1 Fukuura, Kanazawa-ku, Yokohama 236-8643 Japan.
Fax: 045-788-7309;
e-mail: takao.ashikaga@to.shiseido.co.jp

Original paper :AATEX 7(1):30-36,2000
As a simple model of ultraviolet (UV)-induced protein denaturation, Amyloid P hexapeptide (APH, Phe-Thr-Leu-Cys-Phe-Arg) was exposed to UVA irradiation. A new product was isolated by HPLC and identified by fast atom bombardment mass spectrometry (FAB-MS) as the disulfide dimer. Thus, UVA induced disulfide bond formation. We also examined the effect of replacing the Cys residue of APH with other amino acid residues (methionine, tryptophan, tyrosine and histidine) that might be susceptible to oxidative damage. In the case of [Trp4]-APH, the amount of the analog was decresed at 40 J/cm2 or higher. When APH and [Trp4]-APH were mixed and UVA-irradiated, the combination afforded a greater number of products than the sum of those obtained when they were separately irradiated. That finding suggests that denaturation of proteins by UVA may involve very complex reactions of plural kinds of amino acid residues. Since the UV-induced APH dimer formation could be easily evaluated by HPLC, we used this system to examine the effect of antioxidants on the UVA-induced reaction. The dimer formation was greatly inhibited by dithiothreitol and N-acetylcysteine, but was promoted by azide and catechin. This system might be useful for evaluating the ability of drugs to prevent oxidative damage to proteins caused by UVA irradiation.

Keywords: protein denaturation, disulfide bond, oxidative damage, peptide model