Complexes of iron and cobalt tetrasulfonated phthalocyanines with apocytochrome c

Artificial cytochromes c have been prepared with Fe(III) and Co(III) tetrasulfonated phthalocyanines in place of heme. Their structure and properties have been investigated by difference spectroscopy, CD, epr, electrophoresis, molecular weight estimation, and potentiometric measurements. The visible absorption spectra show the main peak at 650 nm for the iron compound 685 nm for the cobalt one. It is shown by CD experiments that incorporation of Fe(III)L or Co(III)L into apocytochrome c markedly increases helical content of the protein. Its conformation is, however, significantly altered as compared with the native cytochrome c. The epr and spectroscopic data show that the iron and cobalt phthalocyanine models represent the low spin species with the metal ions in trivalent state. Electrophoresis and molecular weight estimation indicate these complexes to be monomers. Both phthalocyanine complexes have not affinity for additional ligands characteristic for hemoglobin. They react, however, with CO, NO, and CN- when they are reduced with dithionite. Moreover, Co(II)L-apocyt c is able to combine with oxygen suggesting a structural feature in common with the oxygen-carrying heme proteins. Iron(II) complex in the same conditions is oxidized directly to the ferric state. The half-reduction potentials of Fe(III)L-apocyt c and Co(III)L-apocyt c are +374 mV and +320 mV, respectively. These complexes are reduced by cytochrome c and cytochrome c reductase (cytochrome bc1).