Iron cores of tadpole ferritin: native, reconstituted and recombinant H-chain ferritins

Structural and compositional properties of ferritin cores were studied by transmission electron microscopy (TEM) and inductively coupled plasma (ICP) spectrometry. The native tadpole ferritin (TdF) contains 880 Fe atoms per molecule of protein and considerable amounts of phosphate (Fe:Pi=5.2). The core size of TdF is 6.75 (±0.72) nm. In the ferritin reconstituted with 1170 Fe atoms per molecule of protein, the core size is 8.31 (±0.97) nm. Electron diffraction patterns of both native and reconstituted tadpole ferritins show poor crystallinity, giving diffuse diffraction lines. Both ferritin cores were identified as ferrihydrite. Reconstituted iron cores of recombinant tadpole H-chain ferritin produced in Escherichia coli contain 1280 Fe atoms and show similar crystallinity with the size of 8.08 (±0.90) nm.