Formation of iron(III)-tyrosinate is the fastest reaction observed in ferritin.
Rapid mineralization of ferritin, characteristic of protein with H-type subunits, coincides with formation of a specific Fe(III)-tyrosinate complex. The pseudo-first-order rate constant for Fe(II) oxidation by H-subunit-type ferritin has now been shown to be 700-900 times greater than any previously reported for ferritin; kox = 1000 s-1 for formation of the specific Fe(III)-tyrosinate complex (A550nm) or formation of less defined Fe(III)-oxo multinuclear complexes (A420nm). Formation of multinuclear Fe(III)-oxo complexes and O2 consumption were biphasic. In the first phase, up to 50 Fe atoms/ferritin molecule were rapidly oxidized, accompanied by formation of the Fe(III)-tyrosinate complex; saturation of the sites which formed the Fe(III)-tyrosinate complex also required 50 Fe/ferritin molecule. The sigmoidal shape of the curve obtained by plotting the initial rate of oxidation during the rapid phase of mineralization versus added [Fe(II)] suggested a more complex reaction pathway of ferroxidation than previously described. During the second phase of mineralization, Fe(III)-tyrosinate decreased, but multinuclear Fe(III)-oxo complexes and O2 consumption continued to increase at a slower rate. Recovery of the rapid oxidation pathway paralleled recovery of the site for Fe(III)-tyrosinate formation; full regeneration of the Fe(III)-tyrosinate sites was gradual over a period of 12 h, as if the movement of Fe(III) along the biomineralization pathway in the protein was slow and was accompanied by conformational changes which affected the Fe(III)-tyrosinate site.(ABSTRACT TRUNCATED AT 250 WORDS)
Waldo
G S
GS
Department of Biochemistry, North Carolina State University, Raleigh 27695-7622.
Theil
E C
EC
D000818:Animals; D005290:Ferric Compounds / Q000378:metabolism*; D005293:Ferritins / Q000737:chemistry / Q000378:metabolism*; D005296:Ferrous Compounds / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D011892:Rana catesbeiana; D011994:Recombinant Proteins; D014443:Tyrosine / Q000737:chemistry
D005290:Ferric Compounds; D005296:Ferrous Compounds; D011994:Recombinant Proteins; D014443:Tyrosine; D005293:Ferritins