The formation of ferritin from apoferritin. Kinetics and mechanism of iron uptake

摘要: Ferritin has a high capacity as an iron store, incorporating some 4500 atoms microcrystalline ferric oxide hydrate. Starting from apoferritin, or ferritin of low content, Fe(2+) and oxidizing agent, the uptake can be recorded spectrophotometrically. Progress curves were obtained reconstituted was shown by several physical methods to similar natural ferritin. The progress apoferritin are sigmoidal; those for ferritins content hyperbolic. rate is dependent on amount already present in molecule. distribution contents among molecules inhomogeneous. These findings interpreted terms crystal growth model. surface area crystallites forming inside protein increases until molecule half full, then declines. This controls at which new material deposited. experimental results best accounted two-stage mechanism, initial slow ;nucleation' stage, apparently zero order with respect [Fe(2+)], followed more rapid ;growth' stage. oxidation increased presence compared controls. therefore regarded enzyme product remains firmly attached. appears increase ;nucleation'. apparent this stage suggests binding sites protein, saturated Fe(2+). presumed also sites. subsequent formation hydrate may proceed according one three alternative models.