Photoinduced production of reactive oxygen species by retinal derivatives and conjugates

Abstract

The formation of reactive oxygen species (ROS) during all trans-retinal illumination was studied by ESR. The quantity of ROS was estimated by the ESR signal of a spin adduct of DEPMPO (5-dietoxyphosphoryl-5 methyl-1-pirroline-N-oxide). The ESR signal was found to be a superposition of the adducts: 80%--superoxide anion radical, 15%--hydroxyl radical and 5%--an unknown radical. It was shown that the addition of an equimolar albumin concentration resulted in the 5-fold decrease of the relative quantum yield for ROS generation, and a 4-fold albumin excess led to decreased ROS production by 30-fold. It is supposed that ATR and A2E in the photoreceptor membrane are the sources of photodamage induced by ROS. ATR in the cell is known to be transported by interphotoreceptor retinal binding proteins that belong to the albumin family. The ATR binding with proteins is supposed to prevent the ROS production in the photoreceptor cell and thus produces the light damage protection action.