An investigation of the nature of Bohr, Root, and haldane effects inOctopus dofleini hemocyanin

Summary

• 1. The pH dependence ofOctopus dofleini hemocyanin oxygenation is so great that below pH 7.0 the molecule does not become fully oxygenated, even in pure O₂ at 1 atm pressure. However, the curves describing percent oxygenation as a function of$P_{O_2 }$ appear to be gradually increasing in oxygen saturation, rather than leveling out at less than full saturation. Hill plots indicate that at pH 6.6 and below the molecule is stabilized in its low affinity conformation. Thus, the low saturation of this hemocyanin in air is due to the very large Bohr shift, and not to the disabling of one or more functionally distinct O₂ binding sites on the native molecule.

• 2. Experiments in which pH was monitored continuously while oxygenation was manipulated in the presence of CO₂ provide no evidence of O₂ linked binding of CO₂. While CO₂ does influence O₂ affinity independently of pH, its effect may be due to high levels of HCO ⁻₃ and CO ⁻₃ , rather than molecular CO₂, and it may entail a lowering of the activities of the allosteric effectors Mg²⁺ and Ca²⁺.