Organisms produces reactive oxygen species (ROS) throughout their lives. ROS including superoxide anions, hydroxyl radicals, hydrogen peroxide and singlet oxygen whit known to oxidize biological macromolecules, The accumulation of oxidized, or modified, extra- and intra-cellular proteins in vivo cause age-related diseases such as Parkinson’s disease and cataract. Therefore, it is important to study the damage of proteins by photo-sensitizer. Singlet oxygen is a high reactive oxidant in biology systems, and that proteins are a major target for the damage initiated by this reactive species. Reaction with proteins occurs primarily at Trp, Met, Cys, His, and Tyr side-chains with this resulting in the formation of short-lived endo- or hydroperoxides on Trp, His, and Tyr resi- dues. This paper is a brief introduction about the reactions of singlet oxygen with tyrosine and histidine.
Reactive oxygen species (ROS) induce a lot of disease when the balance breaks between ROS and the enzymic and non-znzymic systems in human body to effectively scavenge ROS and prevent them from damaging the body. Proteins, which account for about 20% dry weight of a human cell, may be major target of attacks by ROS. It has been found that hydroxycinnamic acid, flavonoids and some other natural anti-oxidants can scavenge ROS inside body organs and tissues, and repair effectively oxidization damages to proteins. In recent years, stud- ies have been focused on mechanisms of the ROS caused damages to proteins, and on protecting proteins against ROS. In the meantime, explorations have been made on analyzing stable products of proteins involved in oxidation by ROS and on relationships between scavenging effects of natural anti-oxidants and their molecular structures. However, there are problems remaining before us for answers by still more investigations, such as what is the ROS attacking position on a protein macromolecule and how is the molecular modification of the ROS-attacked protein.
