Protein binding of iron in blood plasma of the ascidian Herdmania momus

Blood of the ascidian Herdmania momus var. grandii (Kott, 1952) has typically a low cell haematocrit volume, <1% with a cell density of 12 000 to 15 000 cells mm^-3. Non-dialysable solids in the plasma are 105±10 mg%. Iron-binding in the plasma has been investigated by fractionation of ⁵⁹Fe-labelled plasma, using gel chromatography and electrophoretic procedures. Three fractions, identified as I, II and III in the order of their elution from a G-150 column, bind ⁵⁹Fe in the ratio 60:15:15. The dominant fraction, I, was shown by electrophoresis on polyacrylamide gels to consist of two components in the ratio of ca. 80:20 and with similar electrophoretic mobilities. Dissociation of Fraction I by mercaptoethanol and sodium dodecyl sulfate gave on electrophoresis three components of molecular weights 17 000; 32 000 and 66 000. Fraction 1 contained 10% carbohydrate by weight as determined by the -cysteine/sulphuric acid assay. These data are compared with other iron-binding systems such as transferrin and the siderophores. Phylogenetic aspects of the study are also discussed.