Abstract
Human serum albumin (HSA) incorporating synthetic tetraphenylporphinato-iron(II) derivatives (FePl orFeP2) can bind and release oxygen reversibly under physiological conditions (in aqueous media, pH 7.4, 37oC). The maximal binding ratio of FePl/HSA was estimated to be eight, and the stepwise equilibrium constants for FePl binding to HSA (K,-K8) ranged from 1.2×106 to 1.3×104 M-1. The major binding sites of FePl are presumably identical to those of hemin, bilirubin and long-chain fatty acids. The O2-binding ability of the HSA-FeP can be regulated by changing the molecular structure of the incorporated hemes. The half-lifetime of the O2-coordinated FeP2 in HSA was significantly longer than that of HSA-FePl.