Modification of isolated α and β chains of human hemoglobin by the metal tetrasulfonated phthalocyanines. Studies on hybrid phthalocyanine-heme intermediates

Abstract

α and β chains of hemoglobin have been modified with cobalt(II) tetrasulfonated phthalocyanine in place of heme. They display properties very similar to those of iron(II) phthalocyanine modified α and β chains. Mixed together they form tetrameric cobalt(II) phthalocyanine hemoglobin. Incorporation of Co(II)L into α and β globins results in stabilization of the protein structure, which is shown by a marked increase in its helicity content. Cobalt phthalocyanine substituted α and β chains are able to combine reversibly with oxygen giving more stable oxygenated species than their native analogues. The rate of both processes is lower in the case of the modified α chain. Recombination of the phthalocyanine α and β chains with the alternate heme containing chains give tetrameric hybrid hemoglobins. These comprise two phthalocyanine modified subunits and two heme containing subunits. The helicity content of the tetrameric hybrid hemoglobin calculated for one subunit is lower that the arithmetic mean of helicities for its isolated subunits. This suggests a destabilizing chain-chain interaction within the tetramer. Unlike in the separated subunits, oxygen binding by hybrid hemoglobins is irreversible. Deoxygenation by argon bubbling leads to the formation of inactive species which in oxygen atmosphere undergo irreversible oxidation with destruction of the complex.