Complexes of iron, cobalt and copper tetrasulfonated phthalocyanines with apomyoglobin

Abstract

The modified myoglobins containing the Fe(III), Co(II) and Cu(II) phthalocyanines in the place of heme were synthetized by recombination of those complexes with apomyoglobin. Such a modification was also carried out by replacement of the heme in myoglobin by metal tetrasulfonated phthalocyanine. This indicates that tetrasulfonated phthalocyanine and porphyrine combine with globin in a similar mode. The structure and properties of the complexes obtained with apomyoglobin were investigated by difference spectroscopy, electrophoresis, molecular weight estimation and the CD method. Absorption spectra show the bands characteristic for these complexes, at 650 nm, 690 nm and 660,700 nm for Fe(III)L-apoMb, Co(II)L-apoMb and Cu(II)-apoMb, respectively. Coordination of iron and cobalt tetrasulfonated phthalocyanine with apomyoglobin increases the helical content of the protein, by 18% and 22%, respectively, to make it more similar to the structure of the native myoglobin. The copper complex shows an increase in disordered structure of about 10% compared with apomyoglobin. Coordination of copper tetrasulfonated phthalocyanine with apomyoglobin is accompanied by a change in the electronic structure of the Cu(II) ion. Deformation of the phthalocyanine complex caused by the cooper ion is responsible for the conformational changes in the protein. In the Soret band and in the VIS the studied compounds produce the induced Cotton effect, which indicates a change in symmetry of the tetrasulfonated phthalocyanine complexes because of the coordination with protein. Molecular weight and electrophoretic results indicate that the synthetized compounds are monomers. Complexes Fe(II)L-apoMb and Co(II)L-apoMb have the ability to perform reversible oxygen fixation and can serve as models of myoglobin. That ability is not preserved in the complexes Cu(II)L-apoMb. The redox properties of the obtained complexes indicate that coordination with apomyoglobin is responsible for stabilization of the II-oxidation state of the metal in the iron and cobalt tetrasulfonated phthalocyanines and for stabilization of the π-electronic system of the phthalocyanine ring in the complex Cu(II)L-apoMb.