Broniec Agnieszka, Pawlak Anna, Sarna Tadeusz, Wielgus Albert, Roberts Joan E, Land Edward J, Truscott T George, Edge Ruth, Navaratnam Suppiah
Department of Biophysics, Faculty of Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Krakow, Poland.
Free Radic Biol Med. 2005 Apr 15;38(8):1037-46. doi: 10.1016/j.freeradbiomed.2004.12.023.
A pyridinium bisretinoid (A2E) is the only identified blue-absorbing chromophore of retinal lipofuscin that has been linked to its aerobic photoreactivity and phototoxicity. Pulse radiolysis has been used to study both the one-electron oxidation and the one-electron reduction of A2E in aqueous micellar solutions. The reduction to the semireduced A2E (lambda(max) broad and between 500 and 540 nm) was achieved with formate radicals and the subsequent decay of A2E* was slow (over hundreds of milliseconds) via complex kinetics. The long lifetime of the A2E* should facilitate its reactions with other biomolecules. For example, with oxygen, the A2E* produced the superoxide radical anion with a rate constant of 3 x 10(8) M(-1) s(-1). The A2E was also reduced by the NAD radical, the corresponding rate constant being 2.3 x 10(8) M(-1) s(-1). Other experiments showed that the one-electron reduction potential of A2E lies in the range -640 to -940 mV. The semioxidized form of A2E (lambda(max) 590 nm) was formed via oxidation with the Br2*- radical and had a much shorter lifetime than the semireduced form. With strongly oxidizing peroxyl radicals (CCl3O2*) our kinetic data suggest the formation of a radical adduct followed by dissociation to the semioxidized A2E. With milder oxidizing peroxyl radicals such as that from methanol, our results were inconclusive. In benzene we observed an efficient oxidation of zeaxanthin to its radical cation by the A2E radical cation; this may be relevant to a detrimental effect of A2E in vision.
吡啶鎓双视黄醛（A2E）是唯一已被确认的视网膜脂褐质中吸收蓝光的发色团，它与视网膜脂褐质的需氧光反应性和光毒性有关。脉冲辐解已被用于研究A2E在水性胶束溶液中的单电子氧化和单电子还原。用甲酸根自由基实现了A2E还原为半还原态A2E（最大吸收波长较宽，在500至540纳米之间），随后A2E通过复杂的动力学缓慢衰减（超过数百毫秒）。A2E的长寿命应有助于其与其他生物分子发生反应。例如，与氧气反应时，A2E生成超氧自由基阴离子的速率常数为3×10⁸ M⁻¹ s⁻¹。A2E也能被NAD自由基还原，相应的速率常数为2.3×10⁸ M⁻¹ s⁻¹。其他实验表明，A2E的单电子还原电位在-640至-940毫伏范围内。A2E的半氧化形式（最大吸收波长590纳米）是通过与Br2自由基氧化形成的，其寿命比半还原形式短得多。对于强氧化性的过氧自由基（CCl3O2*），我们的动力学数据表明会形成自由基加合物，随后解离为半氧化态A2E。对于氧化性较弱的过氧自由基，如来自甲醇的过氧自由基，我们的结果尚无定论。在苯中，我们观察到A2E自由基阳离子能将玉米黄质高效氧化为其自由基阳离子；这可能与A2E对视力的有害影响有关。
