Oxygen-Carrying Plasma Hemoprotein Including Synthetic Heme

Abstract

Recombinant human serum albumin (rHSA) incorporating tetraphenylporphyrinatoiron(II) deriv. with four pivaloylamino substituents (FepivP), albumin-heme, is an entirely synthetic hemoprotein that can reversibly bind and release O2 under physiol. conditions. We have recently found that replacing the substituent groups of FepivP with more hydrophobic 1-methylcyclohexanoylamino groups, affording FecycP, substantially stabilizes the formed O2-adduct complex. The O2- and CO-binding abilities and blood compatibility of this new rHSA-heme hybrid (rHSA-FecycP) have been investigated by spectroscopy. The max. no. of FecycP binding to one albumin was detd. to be eight. Because the isoelec. point and CD (CD) spectral pattern were identical to those of rHSA itself, the two-dimensional structure of the host albumin could be unchanged after the incorporation of FecycP. Laser-flash photolysis expts. gave the assocn. and dissocn. rate consts. for O2 and CO (kon, koff). The rebinding kinetics of these gaseous ligands consists of multiple exponentials. We conjectured that the O2- and CO-binding reactions are affected by the mol. environment around each of the active heme sites. RHSA-FecycP showed almost the same O2-binding affinity(P1/2O2 34 torr at 37°C) and thermodn. parameters (ΔH, ΔS) for the oxygenation as rHSA-FepivP. In contrast, the half-life of the O2-adduct complex (9h, 37°C) became significantly longer than that of rHSA-FepivP (by a factor of 4.5), which is close to that of myoglobin. The obtained red soln. was stable and demonstrated a long shelf life (>2 years) at room temp. The equivalent mixt. of rHSA-FecycP and whole blood exhibited no coagulation or pptn., indicating its high blood compatibility. [on SciFinder(R)]