Functional modulation by lactate of myoglobin. A monomeric allosteric hemoprotein

The effect of lactate on O₂ binding properties of sperm whale and horse heart myoglobins (Mb) has been investigated at moderately acid pH (i.e. pH 6.5, a condition which may be achieved in vivo under a physical effort). Addition of lactate brings about a decrease of O₂ affinity (i.e. an increase of P₅₀) in sperm whale and horse heart myoglobins. Accordingly, lactate shows a different affinity for the deoxygenated and oxygenated form, behaving as a heterotropic modulator. The lactate effect on O₂ affinity appears to differ for sperm whale and horse heart Mb, δlogP₅₀ being ≃1.0 and ≃0.4, respectively. From the kinetic viewpoint, the variation of O₂ affinity for both myoglobins can be attributed mainly to a decrease of the kinetic association rate constant for ligand binding.