IRON BOUND TO FERRITIN CATALYZES ASCORBATE OXIDATION - EFFECTS OF CHELATING-AGENTS

Ferritin is the main intracellular iron storage protein. Ferritin iron may be released by many reducing agents including ascorbate, In this work we report ferritin to catalyze the oxidation of ascorbate. The ki netics of this process were studied in detail in phosphate buffer (pH 7.40): at 37 degrees C by using the Clark electrode technique and ESR. The catalytic effect of ferritin manifested itself as the increase bo th in the rate of oxygen uptake and steady-state concentration of the ascorbate radical. The ferritin catalytic activity was found to be mod ified by iron chelators, EDTA, Desferal (DFO) as well as by ferrozine (FRZ) which is widely used in kinetic studies on ferritin iron release thanks to the formation of a coloured complex with Fe(II). While EDTA promotes the catalytic action of ferritin, DFO and FRZ diminished it. From the comparison of the kinetics of ascorbate oxidation obtained i n the current work and data on the kinetics of ferritin iron release r eported by Boyer and McCleary ((1987) Free Rad. Biol. Med. 3, 389-395) , we conclude that iron bound to ferritin rather than the iron release d is likely responsible for ferritin catalytic action. In addition, it has been concluded that the use of FRZ as an analytical reagent in ki netic studies of reductive ferritin iron release required taking into account the competitive character of the formation of the Fe(II)-FRZ c omplex.