['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.', '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.', '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.'] Is rat duodenal iron-binding protein mobilferrin a homologue of calreticulin?