RELATIONSHIP BETWEEN CIRCULAR-DICHROISM SPECTRA OF LUPIN LEGHEMOGLOBIN DERIVATIVES AND THEIR SPATIAL STRUCTURE

Circular dichroism (CD) spectra in the range of 350-650 nm were studied for a number of ferro- and ferriderivatives of lupin leghemoglobin: Lb(II), LbNO, LbO2, LbCO, LbNb and Lb(III).H2O, LbF, LbAc, LbCN, LbNc, LbIq respectively. It has been found that like soybean leghemoglobin and unlike myoglobin the majority of EC in Soret band has a negative sign, with the exception of LbCO and LbNb where due to the splitting of electron transitions polarized in the heme plane into x- and y-components positive EC appear. In 450-650 nm sometimes the splitting of Q0 and Q1 bands is observed. Changes in CD spectra are considered applying the data on geometry of octahedral complex of heme iron and conformational changes in the protein globule found during X-ray studies of the spatial structures of the complexes under consideration. CD spectra of nitrosobenzene- and oxyleghemoglobin were found to be the most different than the other ones. It is suggested that in the first case the peculiar pattern of the CD curve results from an additional aromatic group incorporated into heme surroundings, significant disturbance of the heme symmetry due to two ligand groups located over its plane and an open conformation of the heme pocket realized in this complex, in the second case - a unique for hemoglobins geometry of the O2 molecule bound as eta-2-ligand. It is shown that the CD spectra are most sensitive to the ligand nature when pi-orbitals of the ligand are included into interactions with iron d-orbitals.