文摘
Apo horse spleen ferritin (apo HoSF) was reconstituted to various core sizes (100-3500 Fe3+/HoSF) by depositing Fe(OH)3 within the hollow HoSF interior by air oxidation of Fe2+. Fe2+ and phosphate(Pi) were then added anaerobically at a 1:4 ratio, and both Fe2+ and Pi were incorporated into the HoSFcores. The resulting Pi layer consisted of Fe2+ and Pi at about a 1:3 ratio which is strongly attached to thereconstituted ferritin mineral core surface and is stable even after air oxidation of the bound Fe2+. Thetotal amount of Fe2+ and Pi bound to the iron core surface increases as the core volume increases up toa maximum near 2500 iron atoms, above which the size of the Pi layer decreases with increasing coresize. Mössbauer spectroscopic measurements of the Pi-reconstituted HoSF cores using 57Fe2+ show that57Fe3+ is the major species present under anaerobic conditions. This result suggests that the incoming57Fe2+ undergoes an internal redox reaction to form 57Fe3+ during the formation of the Pi layer. Additionof bipyridine removes the 57Fe3+ bound in the Pi layer as [57Fe(bipy)3]2+, showing that the bound 57Fe2+has not undergone irreversible oxidation. This result is related to previous studies showing that 57Fe2+bound to native core is reversibly oxidized under anaerobic conditions in native holo bacterial and HoSFferritins. Attempts to bury the Pi layer of native or reconstituted HoSF by adding 1000 additional ironatoms were not successful, suggesting that after its formation, the Pi layer "floats" on the developing ironmineral core.