Iron reductive release was investigated using ferrozine as the Fe2+ chelating as previously reported (Deng et al., 2010). Briefly, the development of [Fe(ferrozine)3]2+ was measured by recording the increase in absorbance at 562 nm using a Varian Cary 50 spectrophotometer (Varian, USA). The rate of iron release from holoferritin (800 Fe3+/protein shell)
was estimated using ε562 = 27.9mM−1 cm−1 as previously described (Deng, Cheng et al., 2010), and the kinetic data were analyzed with Origin 8.0 software (Microcal Inc.).