Human Serum Albumin Incorporating Tetrakis(o-pivalamido) phenylporphinatoiron(II) Derivative as a Totally Synthetic O2-Carrying Hemoprotein

2-[8-{N-(2-Methylimidazolyl)}octanoyloxymethyl]-5,10,15,20-tetrakis(o-pivalamido)phenylporphinatoiron(II)s (FePs) were incorporated into hydrophobic cavities of recombinant human serum albumin (rHSA), providing a totally synthetic O2-carrying hemoprotein (rHSA-FeP). An rHSA host absorbs maximally eight FeP molecules. Solution properties of the obtained albumin hybrid [[rHSA] = 5 wt %; FeP/HSA = 1−8 (mol/mol)] are almost identical to those of the rHSA itself; the specific gravity is 1.013 and the viscosity is 1.1 cP. Circular dichroism spectroscopy and isoelectric focusing measurement revealed that the second-order structure and surface charge distribution of rHSA were always constant independent of the binding numbers of FeP. Hydrophobic interaction is probably a major molecular force of the incorporation of this synthetic heme. rHSA-FeP can bind and release dioxygen reversibly under physiological conditions (in aqueous media, pH 7.3, 37 °C) like hemoglobin and myoglobin. Its O2-coordination structure was evaluated by resonance Raman spectroscopy. The O2 rebinding after the laser flash photolysis showed three-phases decay, which were analyzed by triple-exponential kinetics. The O2-binding affinity and O2-association and -dissociation rate constants of rHSA-FeP satisfy the initial clinical requirements for O2 infusion as a red cell substitute.