Defining the roles of the threefold channels in iron uptake, iron oxidation and iron-core formation in ferritin: a study aided by site-directed mutagenesis.
This paper aims to define the role of the threefold intersubunit channels in iron uptake and sequestration processes in the iron-storage protein, ferritin. Iron uptake, measured as loss of availability of Fe(II) to ferrozine (due to oxidation), has been studied in recombinant human H-chain ferritins bearing amino acid substitutions in the threefold channels or ferroxidase centres. Similar measurements with recombinant horse L-chain ferritin are compared. It is concluded that significant Fe(II) oxidation occurs only at the H-chain ferroxidase centres and not in the threefold channels, although this route is used by Fe(II) for entry. Investigations by Mössbauer and u.v.-difference spectroscopy show that part of the iron oxidized by H-chain ferritin returns to the threefold channels as Fe(III). This monomeric Fe(III) can be displaced by addition of Tb(III). Fe(III) also moves into the cavity for formation of the iron-core mineral, ferrihydrite. Iron incorporated into ferrihydrite becomes kinetically inert.
Treffry
A
A
Racah Institute of Physics, Hebrew University of Jerusalem, Israel.
Bauminger
E R
ER
Hechel
D
D
Hodson
N W
NW
Nowik
I
I
Yewdall
S J
SJ
Harrison
P M
PM
D000595:Amino Acid Sequence; D003124:Colorimetry; D005293:Ferritins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007473:Ion Channels / Q000378:metabolism; D007501:Iron / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D015204:Spectroscopy, Mossbauer; D013725:Terbium / Q000737:chemistry; D015032:Zinc / Q000737:chemistry
D007473:Ion Channels; D011994:Recombinant Proteins; D013725:Terbium; D005293:Ferritins; D007501:Iron; D015032:Zinc