ferritin

^[1]^[2]

Function

major iron storage compound
in hepatocytes & in the macrophage system of the bone marrow & other organs, ferritin provides a reserve of iron readily available for the formation of heme proteins

spherical complex consisting of an apoferritin shell & an interior of [FeOOH]x crystallin core^[2]
another source suggests stored iron is in the form Fe[O{H2PO4}]
the apoferritin shell consists of ~ 24 subunits [variable number of light chains & heavy chains]
in human liver the heavy chain is the major chain
ferritin is about 13 nm in diameter with a central cavity of 7 nm in diameter.
6 pores approximately 0.7-1.0 nm in diameter permit diffusion of small molecules, significantly FMN, ascorbate, & Fe+2
the edges of the pores serve as redox sites for influx & efflux of Fe+2 with storage of FeOOH in the core crystal
he core crystal may contain as many as 4000 Fe atoms, but usually contains 1/2 or less that many^[2]

ferritin is found in nearly all cells of the body
in men, the total body content of stored iron, mostly as ferritin is 800 mg
in healthy women, it ranges from 0-200 mg
minute quantities of ferritin are also present in serum in proportion to total body iron stores, with 1 ng/mL indicating 8 mg of total body iron

serum ferritin levels are increased in relation to total iron stores in fasting, inanition, burns, chronic inflammatory disorders, infections, neoplasms, & in chronic renal disease, increasing the ratio of 1 ng/mL:8 mg total body iron, thus overestimating the total body iron stores.
ferritin levels < 10 ng/mL usually indicate iron deficiency anemia

↑ Tietz Textbook of Clinical Chemistry, 2nd ed. Burtis CA & Ashwood ER (eds), WB Saunders Co, Philadelphia PA, 1993, pg 2060
↑ ^2.0 ^2.1 ^2.2 Wikipedia; Note: ferritin entry http://en.wikipedia.org/wiki/ferritin