Iron storage Iron uptake through the 3-fold channel of<unk> <unk>  is present in every cell type. It serves to store iron in a non-toxic form, to deposit it in a safe form, and to transport it to areas where it is required. The function and structure of the expressed<unk>  protein varies in different cell types. This is controlled primarily by the amount and stability of messenger RNA (mRNA), but also by changes in how the mRNA is stored and how efficiently it is transcribed. One major trigger for the production of many<unk> s is the mere presence of iron; an exception is the yolk<unk>  of Lymnaea sp., which lacks an iron-responsive unit. Free iron is toxic to cells as it acts as a catalyst in the formation of free radicals from reactive oxygen species via the Fenton reaction. Hence vertebrates have an elaborate set of protective mechanisms to bind iron in various tissue compartments. Within cells, iron is stored in a protein complex as<unk>  or the related complex hemosiderin. Apoferritin binds to free<unk> rous iron and stores it in the<unk> ric state. As<unk>  accumulates within cells of the reticuloendothelial system, protein aggregates are formed as hemosiderin. Iron in<unk>  or hemosiderin can be extracted for release by the RE cells, although hemosiderin is less readily available. Under steady-state conditions, the level of<unk>  in the blood serum correlates with total body stores of iron; thus, the serum<unk>  FR5Rl is the most convenient laboratory test to estimate iron stores. Because iron is an important mineral in mineralization,<unk>  is employed in the shells of organisms such as molluscs to control the concentration and distribution of iron, thus sculpting shell morphology and colouration. It also plays a role in the haemolymph of the polyplacophora, where it serves to rapidly transport iron to the mineralizing radula. Iron is released from<unk>  for use by<unk>  degradation, which is performed mainly by lysosomes.<unk> roxidase activity Vertebrate<unk>  consists of two or three subunits which are named based on their molecular weight: L "light", H "heavy", and M "middle" subunits. The M subunit has only been reported in bullfrogs. In bacteria and archaea,<unk>  consists of one subunit type. H and M subunits of eukaryotic<unk>  and all subunits of bacterial and archaeal<unk>  are H-type and have<unk> roxidase activity, which is the conversion of iron from the<unk> rous (Fe2+) to<unk> ric (Fe3+) forms. This limits the deleterious reaction which occurs between<unk> rous iron and hydrogen peroxide known as the Fenton reaction which produces the highly damaging hydroxyl radical. The<unk> roxidase activity occurs at a diiron binding site in the middle of each H-type subunits. After oxidation of Fe(II), the Fe(III) product stays metastably in the<unk> roxidase center and is displaced by Fe(II), a mechanism that appears to be common among<unk> s of all three kingdoms of life. The light chain of<unk>  has no<unk> roxidase activity but may be responsible for the electron transfer across the protein cage. Immune response<unk>  concentrations increase drastically in the presence of an infection or cancer. Endotoxins are an up-regulator of the gene coding for<unk> , thus causing the concentration of<unk>  to rise. By contrast, organisms such as Pseudomonas, although possessing endotoxin, cause plasma<unk>  levels to drop significantly within the first 48 hours of infection. Thus, the iron stores of the infected body are denied to the infective agent, impeding its metabolism. Stress response The concentration of<unk>  has been shown to increase in response to stresses such as anoxia; this implies that it is an acute phase protein. Mitochondria Mitochondrial<unk>  has many roles pertaining to molecular function. It participates in<unk> roxidase activity, binding, iron ion binding, oxidoreductase activity,<unk> ric iron binding, metal ion binding as well as transition metal binding. Within the realm of biological processes it participates in oxidation-reduction, iron ion transport across membranes and cellular iron ion homeostasis. Yolk In some snails, the protein component of the egg yolk is primarily<unk> ; this is a different<unk> , with a different genetic sequence, from the somatic<unk> . It is produced in the midgut glands and secreted into the haemolymph, whence it is transported to the eggs.
Ferritin
Hepcidin
Hemoglobin
Ovoferrin
Lipoic acid
Toxidrome
Plasminogen 
Plasma-lyte