IRON INCORPORATION INTO FERRITINS - EVIDENCE FOR THE TRANSFER OF MONOMERIC FE(III) BETWEEN FERRITIN MOLECULES AND FOR THE FORMATION OF AN UNUSUAL MINERAL IN THE FERRITIN OF ESCHERICHIA-COLI

Iron that has been oxidized by H-chain ferritin can be transferred int o other ferritin molecules before it is incorporated into mature ferri hydrite iron cores. Iron(III) dimers are formed at the ferroxidase cen tres of ferritin H chains at an early stage of Fe(II) oxidation. Mossb auer spectroscopic data now show that the iron is transferred as monom eric species arising from dimer dissociation and that it binds to the iron core of the acceptor ferritin. Human H-chain ferritin variants co ntaining altered threefold channels can act as accepters, as can the f erritin of Escherichia coli (Ec-FTN). A human H-chain ferritin variant with a substituted tyrosine (rHuHF-Y34F) can act as a donor of Fe(III ). Since an Fe(III)-tyrosinate (first identified in bullfrog H-chain f erritin) is absent from variant rHuHF-Y34F, the Fe(III) transferred is not derived from this tyrosinate complex. Mossbauer parameters of the small iron cores formed within Ec-FTN are significantly different fro m those of mammalian ferritins. Analysis of the spectra suggests that they are derived from both ferrihydrite and non-ferrihydrite component s. This provides further evidence that the ferritin protein shell can influence the structure of its iron core.