Rat duodenal iron-binding protein mobilferrin is a homologue of calreticulin

Abstract

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.