Fig. 1.

Protein oxidation resulting in protein carbonyl formation. Reactive oxygen species (ROS) may either react directly with some amino acid residues or lead to oxidative cleavage of the protein backbone. Other possible formation routes of protein carbonyls are via the oxidation of lipids resulting in reactive aldehydes which react with cysteine (Cys), histidine (His), arginine (Arg) and lysine (Lys) residues and thus introduce carbonyl groups and furthermore via the reaction of reducing sugars or their oxidation products with the same residues.