The release of iron from horse spleen ferritin by reduced flavins.
Ferritin-Fe(III) was rapidly and quantitatively reduced and liberated as Fe(II) by FMNH(2), FADH(2) and reduced riboflavin. Dithionite also released Fe(II) from ferritin but at less than 1% of the rate with FMNH(2). Cysteine, glutathione and ascorbate gave a similar slower rate and yielded less than 20% of the total iron from ferritin within a few hours. The reduction of ferritin-Fe(III) by the three riboflavin compounds gave complex second-order kinetics with overlapping fast and slow reactions. The fast reaction appeared to be non-specific and may be due to a reduction of Fe(III) of a lower degree of polymerization, equilibrated with ferritin iron. The amount of this Fe(3+) ion initially reduced was small, less than 0.3% of the total iron. Addition of FMN to the ferritin-dithionite system enhanced the reduction; this is due to the reduction of FMN by dithionite to form FMNH(2) which then reduces ferritin-Fe(III). A comparison of the thermodynamic parameters of FMNH(2)-ferritin and dithionite-ferritin complex formation showed that FMNH(2) required a lower activation energy and a negative entropy change, whereas dithionite required 50% more activation energy and showed a positive entropy change in ferritin reduction. The effectiveness of FMNH(2) in ferritin-Fe(III) reduction may be due to a specific binding of the riboflavin moiety to the protein portion of the ferritin molecule.
D000818:Animals; D001205:Ascorbic Acid; D003545:Cysteine; D004227:Dithionite; D005293:Ferritins; D005415:Flavins; D005978:Glutathione; D006736:Horses; D066298:In Vitro Techniques; D007501:Iron; D007700:Kinetics; D010084:Oxidation-Reduction; D011485:Protein Binding; D012256:Riboflavin; D013154:Spleen; D013816:Thermodynamics
D005415:Flavins; D004227:Dithionite; D005293:Ferritins; D007501:Iron; D005978:Glutathione; D003545:Cysteine; D001205:Ascorbic Acid; D012256:Riboflavin