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referred

• Hemoglobin is the quantitatively predominant heme containing protein in mammals. Its primary function is to bind, transport, and release molecular oxygen. Hemoglobin bound iron remains in the ferrous state during oxygen binding, transport and release. When hemoglobin bound iron is oxidized to ferric iron, it cannot transport oxygen. Oxidized hemoglobin is called methemoglobin.
• Cytochromes are a group of heme containing proteins located in the mitochondria. Their function is the sequential transfer of electrons along the respiratory chain leading to reduction of oxygen to water, and the storage of energy in the form of ATP. The transfer of electrons by cytochromes involves oxidation and reduction cycling of iron.
• Iron exists in a non-heme form as part of succinate dehydrogenase (EC 1.3.99.1), an enzyme that catalyses the formation of fumarate.
• As an enzyme cofactor, iron protects cells from oxidative damage. It exists as a heme component of enzymes such as catalase and peroxidase that catalyze the conversion of peroxides to water.

Iron, a Serum-Free Medium Supplement, Useful In Biomanufacturing; Tissue Engineering and Specialty Media: 
Iron is an essential transition metal in cell culture. It has both beneficial and toxic properties. Consequently, the management of iron levels and delivery are a major challenge. The natural physiological delivery of iron to cells in culture is mediated by transferrin when serum is used. The development of serum-free, animal-protein- and protein-free media has greatly increased the potential for iron toxicity in culture. This is especially critical in biomanufacturing and tissue engineering where iron mediated oxidative and carbonyl stress can alter the chemistry of a cell culture product.

The classical and commercially available media can be divided roughly into three groups: those that do not have iron in the basal formulation: Ames' Medium; Basal Medium Eagle (BME); BGJb Medium Fitton-Jackson Modification; Click's Medium; CMRL-1066 Medium: Fischer's Medium; Iscove's Modified Dulbecco's Medium (IMDM); L-15; McCoy's 5A Modified Medium; Medium 199; RPMI-1640; Swim's S-77 Medium; Waymouth Medium MB; those that contain ferric nitrate: Dulbecco's Modified Eagle's Medium (DMEM); Glascow Modified Eagle's Medium (GMEM); H-Y Medium (Hybri-Max^®); Medium 199; and Williams Medium E; and those that contain ferrous sulfate (generally based on Ham's Nutrient Mixtures): F-12 Coon's Modification; Nutrient Mixture, Ham's F-10; Nutrient Mixture, Ham's F-12; Nutrient Mixture, Ham's F-12 Kaighn's Modification (F12K); MCDB Media; and Serum-Free/Protein Free Hybridoma Medium.

DMEM/Ham's Nutrient Mixture F-12 (50:50) contains both ferric nitrate and ferrous sulfate.

A number of media used as the basis for development of proprietary media useful in biomanufacturing and tissue engineering do not contain iron in their formulae or have been re-engineered specifically to manage iron delivery and toxicity. Proprietaty media developed from Dulbecco's Modified Eagle's Medium (DMEM); Nutrient Mixture, Ham's F-12; and DMEM/Ham's Nutrient Mixture F-12 (50:50) or any other inorganic iron supplemented media typically have the iron salts removed and replaced by a chelated iron. Other important basal media for proprietary media development such as Iscove's Modified Dulbecco's Medium (IMDM) are generally supplemented with a chelated iron.

The management of iron delivery is one of the most complex, yet important, requirements for the development of a suitable cell culture system for biomanufacturing and tissue engineering. Improper iron management affects not only the cell, but also the quality of the cell product. For a more complete discussion of chelated-iron as a cell culture additive go to Sigma's Media Expert.

Iron in Cell Culture