c4c4 c4c4 c4c4 c3c3 c3c3 3 x c 4 axes 4 x c 3 axes o symmetry (no mirror planes)
TRANSCRIPT
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C4
C4
C4
C3
C3
3 x C4 axes4 x C3 axes O symmetry(no mirror planes)
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24 subunuits of4 a-helix bundles
Like an iron malted milk ball!
Fe3+Ox(OH)y core
One bundle
Fe3+O(OH)
Fe2+ oxid
Fe2+ exit
C4
C4
C3
C3
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Fact: At pH 7, [Fe3+] = 10-18 M why?
• Ferritin manages to concentrate ferric ion to mM concentrations (10-3 M).• Lack of gene for ferritin lethal.
Fe3+2O3(H2O)1000 + 5000 H+
Exits from C3 pores
The reaction
2000 Fe2+(H2O)6 + O2 1000 Fe3+—O-O—Fe3+ 2000 Fe3+(H2O)6 + H2O2
fast, msec slow, minutes or hours Enters at C3 pores; ‘translocating mineral precursor’
rxn occurs in subunits
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How and where iron exits from ferritin for cellular use is uncertain. Proline substitution for conserved leucine 134 (L134P) allowed normal assembly but increased iron exit rates. X-ray crystallography of H-L134P ferritin revealed localized unfolding at the 3-fold axis, also iron entry sites, consistent with shared use sites for iron exit and entry. The junction of three ferritin subunits appears to be a dynamic aperture with a "shutter" that cytoplasmic factors might open or close to regulate iron release in vivo.
Localized unfolding at the junction of three ferritin subunits. A mechanism for iron release?Takagi, H., Shi, D., Ha, Y., Allewell, N.M., Theil, E.C. (1998) J.Biol.Chem. 273: 18685-18688
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