Ferritin – Structure

  • Ferritin is a multisubunit protein with an outer protein shell and an inner cavity (protein cage) in which iron is stored in the Fe3+ form as ferrihydrite (inner mineral core).1
  • The apoferritin shell has a molecular weight of about 450 kDa and a 7.0 nm-diameter internal cavity.2
  • When fully saturated, a ferritin molecule can store up to 4500 atoms of iron, but the usual amount is closer to about 2000 atoms.3
  • Ferritin is heterogeneous, differing between cell types and tissues in:
    • Relative proportion of the different monomer subunits
    • Iron content of its core
    • Amount of carbohydrate
  • By electron microscopy:4
    • Iron-containing ferritin molecules are readily detected because of the electron density of the core.
    • Typically, the particles have an octahedral appearance
    • Ferritin molecules with maximal iron deposition in the core appear larger on electron micrographs
    • Cytoplasmic ferritin may:
      • Be randomly dispersed
      • Occur in clusters
      • Occur in lysosomes (termed siderosomes)
  • Apoferritin refers to the iron-free form of the protein; the iron-containing form is termed holoferritin or simply ferritin.
Ferritin is a hollow protein shell composed of 24 subunits. Two subunits have been removed to allow visualization within the core where up to 4500 iron atoms can be stored. Source.
High magnification electron microscopic image of peribiliary area of liver showing cluster of ferritin particles. Source.
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