Role of phosphate and kinetic characteristics of complete iron release from native pig spleen ferritin-Fe

The kinetics for complete iron release showing biphasic behavior from pig s pleen ferritin-Fe (PSFF) was measured by spectrophotometry. The native core within the PSFF shell consisted of 1682 hydroxide Fe3+ and 13 phosphate mo lecules. Inhibition kinetics for complete iron release was measure by diffe rential spectrophotometry in the presence of phosphate; the process was cle arly divided into two phases involving a first-order reaction at an increas ing rate of 46.5 Fe3+/PSFF/min on the surface of the iron core and a zero-o rder reaction at a decreasing rate of 6.67 Fe3+/PSFF/min inside the core. T he kinetic equation [C(PSFF-Fe3+)(max) - C(PSFF-Fe3+)(t)](1/2) = T-max -T-t gives the transition time between the two rates and represents the complex kinetic characteristics. The rate was directly accelerated twofold by a mi xed reducer of dithionite and ascorbic acid. These results suggest that the channel of the PSFF shell may carry out multiple functions for iron metabo lism and storage and that the phosphate strongly affects the rate of iron r elease.