Published online by Cambridge University Press: 11 May 2009
Measurements of pH, oxygen content, O2-combining capacity, and haemoglobin concentration were made for the vascular blood of the burrowing polychaete Neoamphitrite figulus in order to assess the role of its two respiratory pigments in respiration. The oxygen equilibrium curve of the erythrocruorin (extracellular haemoglobin) in the vessels was sigmoidal, having an n50 value of 1·5 and a low affinity for oxygen as determined by the P50 which was 26 mmHg at pH 7·31 and 18 °C. O2-binding by the erythrocruorin is sensitive to changes in pH (Δ log P50/Δ log pH = –0·24 to –0·29). The coelomic cell haemoglobin has a hyperbolic equilibrium curve (n50 = 1·0) and a high affinity for oxygen (P50 = 4·5 mmHg) independent of pH, suggesting an oxygen transfer system from the erythrocruorin to the coelomic cells.
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