A mono-sited transferrin from a representative deuterostome: the ascidian
Pyura stolonifera (subphylum Urochordata)
AW Martin, E Huebers, H Huebers, J Webb and CA Finch
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 lambda = 280 and lambda =
429 nm (E429/E280 = 0.044). Bicarbonate is bound concomitantly with high
affinity and is necessary for optimal color formation at lambda = 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.
Volume 64,
Issue 5,
pp. 1047-1052,
11/01/1984
Copyright © 1984 by The American Society of Hematology
