Properties of Ferritin and Hemosiderin Present in Healthy Brain Tissue

As mentioned above, the Mossbauer spectra of iron in all three brain structures studied, showed only ferritin-like, high-spin trivalent iron. There has been one spectrophotometry study that claimed about 75% of the iron in control SN (and about 50% of iron in parkinsonian SN) is divalent [15]. Such a high percentage of divalent iron could not escape detection by MS. Computer simulations, aimed at determining the concentration of divalent iron in the tissues that could escape detection by MS, showed this to be at most 5% [5]. Analysis of the procedure of the sample preparation for spectrophotometry lead us to the suspicion that the high concentration of divalent iron found in this experiment may have been due to the destruction of the protein shell of ferritin by hydrochloric acid and pepsin, which may have caused an efflux of iron from ferritin. It may be that this iron was then reduced from trivalent to divalent iron by ascorbic acid present in the cells. Indeed, tissues pretreated in this way and assessed by MS did show large concentrations of divalent iron [16]. 

4 PROPERTIES OF FERRITIN AND HEMOSIDERIN PRESENT IN HEALTHY BRAIN TISSUE 

Ferritin is an iron-storage protein, which keeps iron in a safe form within a protein shell. The protein shell of mammalian ferritin is composed of 24 subunits of heavy (H)and light (L) amino acid chains. The external diameter of the protein shell is about 12 nm, and the diameter of the internal cavity is about 7 nm. Inside this cavity up to 4500 ions of iron may be located. Most of the ferritin molecules are not full, but contain varying amounts of iron [IT]. 

Hemosiderin is a much less studied molecule. It is generally considered a product of the degradation of ferritin [IT]. The diameters of the iron cores of ferritin and of hemosiderin were determined by electron microscopy on ferritin and hemosiderin isolated from the tissues. As presented in the table, the average diameters of the cores are significantly smaller in brain ferritin and hemosiderin than in liver ferritin and hemosiderin (3.1-3.7 nm versus 6.0 nm and 2.0 05 nm versus 3.5 nm, respectively) [19]. 

The above-presented properties of brain ferritin and hemosiderin suggest a different metabolism of iron in the brain and in organs such as the liver. As the H-ferritin subunits are involved more than L subunits in taking up and possibly also in releasing iron from ferritin, the significantly higher H/L ratio in the brain may possibly point to a higher turnover of iron in the brain [22]. 

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