Ferritin - molecular model

The iron storage molecule ferritin consists of 24 subunits arranged in a spherical shell around a central cavity. Excess free iron is toxic and each ferritin molecule stores up to 4500 iron atoms inside its cavity as an insoluble and harmless iron (III) hydroxide. Each subunit consists of four long alpha helices and one short one, shown schematically as cylinders. Each subunit is shown in a different colour.