A MONO-SITED TRANSFERRIN FROM A REPRESENTATIVE DEUTEROSTOME - THE ASCIDIAN PYURA-STOLONIFERA (SUBPHYLUM, UROCHORDATA)

  • 1 January 1984
    • journal article
    • research article
    • Vol. 64  (5) , 1047-1052
Abstract
An Fe-binding protein was found in the plasma of P. stolonifera. This protein has a MW of about 41,000 .+-. 2000 and binds 1 mol Fe 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 Fe with human apotransferrin under physiologic conditions over 2 h. Upon incubation with rat reticulocytes, the protein reacts with membrane receptors for transferrins, and the proteins, with its Fe, is transported intracellularly where the Fe is incorporated into heme. The 59Fe protein, after i.v. 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 2 Fe-binding sites, resulted from a gene duplication.