FUNCTIONAL MODULATION BY LACTATE OF MYOGLOBIN - A MONOMERIC ALLOSTERIC HEMOPROTEIN

The effect of lactate on O-2 binding properties of sperm whale and hor se 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 physica l effort). Addition of lactate brings about a decrease of O-2 affinity (i.e. an increase of P-50) 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 O-2 affinity appears to differ for sperm whale and horse he art Mb, delta logP(50) being approximate to 1.0 and approximate to 0.4 , respectively. From the kinetic viewpoint, the variation of O-2 affin ity for both myoglobins can be attributed mainly to a decrease of the kinetic association rate constant for ligand binding.