[Lupine leghemoglobin affinity to ligands. The effect of pH and buffer nature]

The myoglobin-like haemoprotein leghaemoglobin (Lb I) from lupine root nodules has a great affinity to molecular oxygen and seems to be involved in O2-transport. Some ligands of low molecular weight are supposed to affect the haemoglobin (Hb) and myoglobin (Mo) function in O2-transport. To investigate this possibility for lupine Lb I, the affinity of this protein to cyanide (CN-), azide (N3-), fluoride (F-), thiocyanate (NCS-), imidazole (Im), nicotinic acid (NA), acetic acid has been investigated, using: 0.05 M MES, pH 5.2-6.5; 0.1 M Na-phosphate in 0.05 M Tris-buffer, pH 6.5-9.0. The affinity for Lb I to N3-, CN-, F- and NA (the Bohr effect) was found to be pH-dependent. The values of PK ionization for the groups affecting the ligands binding were determined. The positive correlation between the ligand affinity and the ligand power was found. Lb I appears to have the greatest ligand affinity constants when compared with other haemoproteins of this class.