O₂-binding properties of albumin hybrid incorporating porphyrinatoiron having histidine derivative

We have evaluated the dioxygen binding properties of albumin hybrid incorporating porphyrinatoirons having histidine derivative [FeP(His), FeP(MHis)]. They were synthesized via 9 steps from 5,10,15,20-tetrakis(o- aminophenyl)porphyrin. FeP(His) binds histidine and FeP(MHis) binds 1-methylhistidine as a proximal base. Both hemes could be incorporated into human serum albumin (HSA) providing HSA hybrid [HSA-FeP(His) or HSA-FeP(MHis)] in the buffer solution (pH 7.3). HSA-FeP(MHis) showed a low O ₂-binding affinity (P₅₀: 15 Torr) and a high O ₂-dissociation rate constant in comparison to HSA-FeP(His). This is due to the steric hindrance for the coordination of the proximal base derived from the methylene group at 4-posititon of imidazole ring in FeP(MHis). HSA-FeP(MHis) can be utilized as a new artificial O₂-therapeutics.