Dynamics of oxygen binding to modified iron(II)-porphyrin complexes embedded in the bilayer of phospholipid liposome

Activation parameters have been determined for the binding of oxygen to 5,10,15,20-tetra{α-o-[2′,2′-dimethyl-20′-(2″- trimethylammonioethylphosphonatoxy)eicosanamido]phenyl}porphyrinato-iron(II) (lipid-heme) and 5,10,15,20-tetra(α-o-pivalamidophenyl)porphyrinatoiron(II) (heme) complexes of 1-lauryl-2-methylimidazole embedded in the bilayer of phospholipid liposome (abbreviated liposome-embedded lipid-heme and heme, respectively). Activation parameters, ΔH‡_on and ΔS‡_on, for the liposome-embedded lipid-heme were consistent with those of hemoglobin and myoglobin, but those for the liposome-embedded heme were similar to those of red blood cells. A potential energy diagram and binding pathway for the oxygen-binding reaction to the Iiposome-embedded lipid-heme and to the liposome-embedded heme are discussed in comparison with those of hemoglobin.