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

The Baltic benthic amphipod Monoporeia affinis (Lindström) 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 P₅₀ of 4 kPa at pH?7.5 (6?°C). The Bohr factor (Δlog P₅₀/ΔpH) is also low, ?0.51, and the cooperativity coefficient, n₅₀, at P₅₀ 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.