Ferritin iron content

In rats, the hepatic xanthine oxidase is absent in the fetus and the newborn and appears only after birth. Normally, ferritin iron content in liver is high before birth and decreases after birth when the xanthine oxidase activity appears in the liver. The ferritin iron stores remain low during weaning but increase when an iron-containing diet is taken. 

Synthesis of the transferrin receptor (TfR) and that of ferritin are reciprocally linked to cellular iron content. Specific untranslated sequences of the mRNAs for both proteins (named iron response elements) interact with a cytosolic protein sensitive to variations in levels of cellular iron (iron-responsive element-binding protein). When iron levels are high, cells use stored ferritin mRNA to synthesize ferritin, and the TfR mRNA is degraded. In contrast, when iron levels are low, the TfR mRNA is stabilized and increased synthesis of receptors occurs, while ferritin mRNA is apparently stored in an inactive form. This is an important example of control of expression of proteins at the translational level. 

For all these techniques, the general qualitative correlation between the measured parameter and the iron concentration was established. However, the measurements are too sensitive to the parameters of the experimental procedures and to physiological data beyond the iron content to allow for routine use in hospitals (43). Indeed, the relaxivity of ferritin is different in solutions, in the liver, in the spleen, in the brain, etc., which implies that MRI quantification protocols must be developed separately for each organ. 

Known compositional variations of ferritin iron cores only Involve phosphate, which can range from as much as 80% (21) to as little as 5% of the iron (21) in normal mammalian liver or spleen, the amount of phosphate in the ferritin iron core is ca. 12% of the iron (24). When the phosphate content is high, the distribution of phosphate is clearly throughout the core rather than on the surface. However, interior locations for phosphate are also suggested when the phosphate content is lower, by data on an Fe(III)ATP model complex (P Fe 1 4) (25) or by phosphate accessibility studies in horse spleen ferritin (P Fe = 1 8) (24). Based on model studies, other possible variations in core composition could Include H2O or sulfate (26). 

The possible role of the mycobactins in the storage of iron in the mycobacteria has been noted. Of greater significance is the identification of ferritin-like molecules in some bacteria. The cytochrome 6557.5 from Azotobacter vinelandii, known to be associated with large amounts of iron, is now known to be a ferritin, with an iron content of 13-20% and an electron-dense core of... 

In the off-resonance region the radius of gyration is 42 A. This value lies well between those of iron-free apoferritin (51.5 A) and full ferritin (28 A) As saturated ferritin contains about 4300 iron atoms, an average iron content of about 3000 iron atom is estimated for this ferritin sample. From Eq. (65) and with reference to the radius of gyration of the FeOOH core, R = 28 A, the relative increase of R at the K-absorption edge indicates 14% decrease of the contrast q of ferritin, due to the anomalous dispersion of iron. The scattering density of the core decreases by as much as 17% and the atomic form factor of iron changes its value by one quarter (7 electrons in f ). 

Ferritin is present in the blood in very low concentration. Although it is an acute phase protein, under normal conditions it roughly reflects the body iron content. The circulating protein is iron poor and largely consists of iron-poor, glycosylated L chains it is largely apoferritin. The plasma fer-... 

Native apoferritin can be prepared by a number of centrifugal methods. Density gradient centrifugation (62) in isopycnic gradients of CsCl or in sucrose have been used to fractionate native ferritin according to its iron content. The native apoferritin sediments with a buoyant density of 1.23, whilst full ferritin has a density in excess of 1.8. Typically using an SW 27 rotor 100 hr are required at 25.000 rpm with a CsCl... 

Ferritin consists of a shell of protein subunits surrounding a core of ferric hydroxyphosphate. For some time the inorganic component of ferritin was thought to be attached to the surface of the protein (65). However, the demonstration that ferritin and apoferritin have the same electrophoretic mobilities and are precipitated equally well with horse ferritin antibody (66) together with electron microscopic evidence (67) clearly showed that the iron is concentrated in the middle of the apoferritin protein shell. The iron micelle has a diameter of 70—75 A whilst the protein shell has a diameter of the order of 120 A (67—70, 62). Somewhat lower values are found in dried preparations (71, 72). The micelle contains ferric iron, predominantly as (FeO.OH) but also with some 1—1.5% phosphate (4,50) and it seems that the iron phosphorus ratio is constant for ferritins of different iron content (52). The composition (FeO.OH) g. (FeO.OPOgHg) has been suggested (73, 74). The percentage of iron in the micelle on this basis is 57%. 

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