Studies on Ligand Binding of Kidney Bean Leghemoglobin.

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Abstract
Absorption spectra of different ligand derivatives of kidney bean [Phaseolus vulgaris] leghemoglobin a were recorded. The effect of pH on the absorption spectra of kidney bean leghemoglobin a was studied. The pK of the acid-alkaline transition of the heme-linked water molecule is 8.25 and the pK for the acid dissociation of the heme group is 4.03. Affinities of kidney bean leghemoglobin for 2 different types of ligands were studied in comparison with soybean leghemoglobins a and c and sperm whale myoglobin. All these leghemoglobins have similar affinities for the small anionic ligand flurine ion, and they are only slightly more accessible to this ligand than is sperm whale myoglobin. Differences in the primary structure or in conformation of these proteins are reflected in the affinity for the bulky ligand imidazole. The accessibility to imidazole increases in the order sperm whale myoglobin .mchlt. soybean Lba < soybean Lbc < kidney bean Lba, and also low spin Lba < high spin Lba. The results are discussed with respect to the amino acid sequences of the leghemoglobins.