Rat duodenal iron-binding protein mobilferrin is a homologue of calreticulin.
BACKGROUND
Mobilferrin is a water soluble 56-kilodalton protein isolated from human and rat duodenal mucosa. It binds iron and other transitional metals in vivo and in vitro and is postulated to play a role in their absorption and intracellular metabolism. The purpose of this study was to characterize mobilferrin.


METHODS
Mobilferrin was characterized by identification of the N-terminal amino acid sequence, two-dimensional protein electrophoresis, and studies of mobilferrin and homologues using anti-mobilferrin antibody and competitive metal binding.


RESULTS
The N-terminal amino acid sequence of mobilferrin was Asp-Pro-Ala-Ile-Tyr-Phe-Lys-Glu-Gln-Phe-Leu-Asp-Gly-Asp-Ala-Ser-Thr- and is a homologue of calreticulin (calregulin). The proteins had a similar molecular mass (56 kilodalton) and isoelectric point (4.7). Anti-mobilferrin antibodies react with calreticulin. Both proteins bind iron and calcium but have a greater affinity for iron.


CONCLUSIONS
Mobilferrin and calreticulin are homologues that bind iron with greater affinity than calcium and other transitional metals. Competitive binding of metals by mobilferrin provides insight into the absorptive pathway shared by both essential and toxic transitional metals.
Department of Medicine, University of South Alabama, Mobile.
M E
ME
Conrad
J N
JN
Umbreit
E G
EG
Moore
D000595:Amino Acid Sequence; D000818:Animals; D002135:Calcium-Binding Proteins / Q000737:chemistry*; D037282:Calreticulin; D002352:Carrier Proteins / Q000737:chemistry / Q000302:isolation & purification* / Q000502:physiology; D004386:Duodenum / Q000737:chemistry*; D007501:Iron / Q000378:metabolism*; D033862:Iron-Binding Proteins; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011817:Rabbits; D051381:Rats; D017386:Sequence Homology, Amino Acid; D033863:Transferrin-Binding Proteins
D002135:Calcium-Binding Proteins; D037282:Calreticulin; D002352:Carrier Proteins; D033862:Iron-Binding Proteins; D033863:Transferrin-Binding Proteins; D007501:Iron