A Mono-sited Transferrin From a Representative Deuterostome: The Ascidian Pyura stolonifera (Subphylum Urochordata)

• Published in: Blood Vol. 64; no. 5; pp. 1047 - 1052
• Main Authors: Martin, A.W., Huebers, E., Huebers, H., Webb, J., Finch, C.A.
• Format: Journal Article
• Language: English
• Published: Washington, DC Elsevier Inc 01.11.1984; The Americain Society of Hematology
• Subjects: Analytical, structural and metabolic biochemistry; Animals; Biological and medical sciences; Feces - analysis; Fundamental and applied biological sciences. Psychology; Iron - analysis; Kidney - metabolism; Mammals; Metalloproteins; Other metalloproteins; Proteins; Receptors, Cell Surface - metabolism; Receptors, Transferrin; Reticulocytes - metabolism; Transferrin - analysis; Transferrin - metabolism; Transferrin - urine; Urochordata - analysis; Ferroprotein; Transferrin; Biological evolution; Iron; Binding site; Prochordata; Invertebrata; Physicochemical properties; Urochordata
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V64.5.1047.1047

An iron-binding protein has been found in the plasma of Pyura stolonifera. This protein has a molecular weight of about 41,000 ± 2,000 and binds 1 mol iron/mol protein. The absorption maxima are λ = 280 and λ = 429 nm (E429/E280 = 0.044). Bicarbonate is bound concomitantly with high affinity and is necessary for optimal color formation at λ = 429 nm. The protein showed a negligible exchange of iron with human apotransferrin under physiologic conditions over two hours. Upon incubation with rat reticulocytes, the protein reacts with membrane receptors for transferrins, and the protein, with its iron, is transported intracellularly where the iron is incorporated into heme. The 59Fe protein, after intravenous injection, disappears rapidly from the plasma and is excreted largely in the urine, with a substantial fraction present in the kidney and another large fraction present in the gut. These findings established the protein as a “transferrin” and support the concept that the larger transferrin molecule in vertebrates, with two iron-binding sites, resulted from a gene duplication.