Structural studies of iron and cobalt tetrasulfonated phthalocyanine-globin complexes

The structure of the complexes of iron and cobalt tetrasulfonated phthalocyanines with globin has been investigated by circular dichroism (CD), electron paramagnetic resonance (EPR) and polyacrylamide gel electrophoresis. Electrophoretic investigations and the molecular weight estimation indicates that the model complexes in the solutions are dimers. It is evident from the results of CD measurements that the incorporation of the iron or cobalt tetrasulfonated phthalocyanine into apohemoglobin significantly increases the helical structure of the protein and causes an appearance of the induced Soret and visible Cotton effects. Unlike methemoglobin, several discrete transition energies in the CD Soret band of Fe(III)L-globin are observed which suggest an inequivalence of the subunits within this complex. This suggestion is supported by EPR studies, which show that the iron atoms in Fe(III)L-globin are in two low electronic states. Electronic structures of the cobalt ions in Co(II)L-globin and oxyCo(II)L-globin are similar to those of coboglobin and oxycoboglobin, respectively, as is proved by EPR results. On this basis we conclude that the oxygen adduct of Co(II)L-globin can be described as a superoxide ion corrdinated to a formally cobaltic phthalocyanine compound.