The subunits of Abarenicola affinis affinis (Ashworth) extracellular haemoglobin (erythrocruorin)

The subunits of the erythrocruorin of Abarenicola affinis affinis (Ashworth) were investigated by various physicochemical methods. Gel chromatography at pH 9.0 in Sephadex G-200 gave three main protein peaks with molecular weights of 240 000, 100 000 and 31 000, respectively. Polyacrylamide gel electrophoresis showed considerable heterogeneity in the subunits, although the main components gave similar molecular weight ranges to the above. Anomalous results were also obtained in SDS-polyacrylamide gel electrophoresis. In the analytical ultracentrifuge, the subunit from the first peak showed a sedimentation coefficient of 10 S and Mw 250 000, and the second yielded s20,w = 5 S. Functionally, the 10 S subunit showed cooperative oxygen binding, but the Hill coefficient was lower than that observed for the native molecule. A possible model for the subunit structure of Abarenicola affinis affinis erythrocruorin is discussed.