HEME TRANSFER-REACTIONS - AN IMPORTANT PREREQUISITE FOR SYNTHETIC OXYGEN CARRIERS

Electronic changes of iron-and metal free porphyrins are reviewed in l ight of their importance to modify the ferri/ferro reduction potential and energy dissipation between ligated carbon monoxide and the porphy rin chelate. Substitutions at positions 2 and 4 are effective ways to exercise this influence. Other measures include exposure to water and modifications of axial ligation, including the 'three-ligand' case. Th ese measures will also influence the stability of recombined hemin-pro tein entities, as apparent from the kinetics of heme-transfer from a m odified donor protein to apomyoglobin, but the stability appears to be related to the bulkiness of 2,4-substitutional groups rather than to electron availability. It is suggested that the altered stability is a secondary effect from enhanced exposure to water in the crevice.