Reduction and release of ferritin iron by plant phenolics.

The reductive release of ferritin iron by several naturally occurring o-diphenols was studied. The initial rate of iron release was quantified by spectrophotometric measurement of the Fe(ferrozine)3(2+) complex, which absorbs maximally at 562 nm. The initial rate of iron release was dependent upon o-diphenol concentration, but not on the concentration of the chromophoric chelating agent, ferrozine, Stoichiometric measurements resulted in a ratio of 2Fe(II) released per molecule of o-diphenol. The series of o-diphenols studied included, caffeic acid, chlorogenic acid, dihydrocaffeic acid, 3,4-dihydroxybenzoic acid, and several analogs. These reductants represent an oxidation reduction potential range of 0.38 volts. A direct correlation between reducing power of the o-diphenols and rate of ferritin iron release was observed. Superoxide dismutase, catalase, mannitol, or general radical traps had no effect on the rate of iron removal; however, EDTA and oxalate inhibited iron release. A mechanism for ferritin iron reduction and release by o-diphenols consistent with the experimental observations is discussed.