牛血清白蛋白的光损伤和光氧化机理

Photodamage and Photooxidation Mechanisms of Bovine Serum Albumin

运用激光闪光光解瞬态吸收技术,在266nm激光激励下,研究了牛血清白蛋白(BSA)光损伤和被SO4-●单电子氧化的反应机理,表征了反应过程中生成的自由基.结果表明,在266nm激光照射下,BSA可同时发生光电离和光激发,生成色氨酸阳离子自由基(Trp/NH+●),由Trp/NH+●快速脱质子形成的色氨酸中性自由基(Trp/N●)及色氨酸三重激发态(3Trp*),3Trp*再与酪氨酸(Tyr)发生分子内电子转移生成酪氨酸中性自由基(Tyr/O●).在SO4-●单电子氧化的反应中,借助减谱技术,求得BSA中Tyr和色氨酸(Trp)自由基的表观生成速率常数,但未发现分子内电子转移现象,阐明了SO4-●自由基是通过与BSA中的Tyr和Trp发生电子转移反应来氧化BSA的,SO4-●氧化BSA的反应速率常数为1.51×1010L·mol-·1s-1,从而为进一步研究血清白蛋白的氧化还原代谢过程提供理论基础.

Photodamage and photooxidation mechanisms of bovine serum albumin （BSA） as induced by UV radiation and one-electron oxidation by SO4^-· were investigated by 266 nm laser flash photolysis. BSA can be photoionized and photoexcited by 266 nm photons to give tryptophan （Trp）/NH^＋·, TIP/N^· resulting from the rapid deprotonation of Tip/ NH^＋·, and ^3Tip^·. Through intermolecular electron transfer between ^3Trp^· and tyrosine （Tyr）, Tyr/O^· was produced. In one-electron oxidation of BSA by SO4^-· the apparent set up rate constants of Tyr and Tip radicals were calculated but intermolecular electron transfer was not observed. We propose that SO4^-· oxidizes BSA by electron transfer to the Tyr and Tip of BSA with a rate constant of 1.51×10mL·mol^-1·s^-1. This research provides an introductory theory to enable further study on the redox metabolic process of BSA.