The iron oxidation and hydrolysis chemistry of Escherichia coli bacterioferritin.
Bacterioferritins are members of a class of spherical shell-like iron storage proteins that catalyze the oxidation and hydrolysis of iron at specific sites inside the protein shell, resulting in formation of a mineral core of hydrated ferric oxide within the protein cavity. Electrode oximetry/pH stat was used to study iron oxidation and hydrolysis chemistry in E. coli bacterioferritin. Consistent with previous UV-visible absorbance measurements, three distinct kinetic phases were detected, and the stoichiometric equations corresponding to each have been determined. The rapid phase 1 reaction corresponds to pairwise binding of 2 Fe(2+) ions at a dinuclear site, called the ferroxidase site, located within each of the 24 subunits, viz., 2Fe(2+) + P(Z) --> [Fe(2)-P](Z) + 4H(+), where P(Z) is the apoprotein of net charge Z and [Fe(2)-P](Z) represents a diferrous ferroxidase complex. The slower phase 2 reaction corresponds to the oxidation of this complex by molecular oxygen according to the net equation: [Fe(2)-P](Z) + (1)/(2)O(2) --> [Fe(2)O-P](Z) where [Fe(2)O-P](Z) represents an oxidized diferric ferroxidase complex, probably a mu-oxo-bridged species as suggested by UV-visible and EPR spectrometric titration data. The third phase corresponds to mineral core formation according to the net reaction: 4Fe(2+) + O(2) + 6H(2)O --> 4FeO(OH)((core)) + 8H(+). Iron oxidation is inhibited by the presence of Zn(2+) ions. The patterns of phase 2 and phase 3 inhibition are different, though inhibition of both phases is complete at 48 Zn(2+)per 24mer, i.e., 2 Zn(2+) per ferroxidase center.
Yang
X
X
Department of Chemistry, University of New Hampshire, Durham, New Hampshire 03824, USA.
Le Brun
N E
NE
Thomson
A J
AJ
Moore
G R
GR
Chasteen
N D
ND
D019943:Amino Acid Substitution / Q000235:genetics; D001059:Apoproteins / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins; D001665:Binding Sites; D002374:Catalase / Q000378:metabolism; D002570:Ceruloplasmin / Q000378:metabolism; D003573:Cytochrome b Group / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000737:chemistry*; D005290:Ferric Compounds / Q000378:metabolism; D005293:Ferritins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D005296:Ferrous Compounds / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis / Q000187:drug effects; D007501:Iron / Q000378:metabolism*; D007700:Kinetics; D009154:Mutation / Q000235:genetics; D010084:Oxidation-Reduction / Q000187:drug effects; D010100:Oxygen / Q000378:metabolism*; D011522:Protons; D013053:Spectrophotometry; D017186:Titrimetry; D015032:Zinc / Q000494:pharmacology
D001059:Apoproteins; D001426:Bacterial Proteins; D003573:Cytochrome b Group; D005290:Ferric Compounds; D005296:Ferrous Compounds; D011522:Protons; D005293:Ferritins; C018032:bacterioferritin; D006861:Hydrogen Peroxide; D007501:Iron; D002374:Catalase; D002570:Ceruloplasmin; D015032:Zinc; D010100:Oxygen