OXYGEN-TRANSPORTING FUNCTION OF HEMOGLOBIN IN DAPHNIA-MAGNA

The in vivo oxygenation of hemoglobin (Hb) in living Daphnia magna was studied at various oxygen pressures by an optical method. Two populations were studied: a normoxia-adapted (Hb-poor) population, and a hypoxia-adapted (Hb-rich) population. The enhancement of Hb oxygenation caused by adding 2 mM KCN to completely inhibit cell respiration was measured to clarify the oxyen-transporting function of Hb in the two groups. Hemoglobulin was 50% oxygenated in vivo at ambient oxygen pressures of 15 and 35 torr for Hb-rich and Hb-poor animals, respectively. In the presence of KCN, 50% oxygenation occurred at ambient oxygen pressures of 7.5 and 14 torr for Hb-rich and Hb-poor animals, respectively.