Oxygen-binding properties of haemolymph from the benthic amphipod Monoporeia affinis from the Baltic

The Baltic benthic amphipod Monoporeia affinis (Lindstrom) has haemocyanin as a respiratory pigment. Haemocyanin constitutes ca. 90% of the total protein in the haemolymph. Oxygen affinity of the pigment is low, a P-50 of 4 kPa at pH 7.5 (6 degrees C). The Bohr factor (Delta log P-50/Delta PH) is also low, -0.51, and the cooperativity coefficient, n(50), at P-50 is 1.5 to 2.5. The pigment characteristics point to a modest role of the haemocyanin, contrary to what could be expected for this sediment-living amphipod. It is suggested that physically dissolved oxygen is most important as oxygen supplier to the tissues.