Photoacoustic calorimetry and transient absorption have been used to characterize thermodynamic and kinetic parameters and time-resolved volume and enthalpy changes for oxygen photorelease from hemoglobin (Hb) complexed with allosteric effectors and in various buffer solutions. Under stripped conditions we observe a significant temperature dependence of enthalpy and volume changes associated with oxygen photorelease. Upon photolysis at low temperatures we observe an endothermic enthalpy and volume expansion of the protein (272 � 60 kcal mol-1, 19.5 � 4.5 mL mol-1), while at high temperatures we observe an exothermic enthalpy and volume contraction (-252 � 79 kcal mol-1, -58.3 � 16.5 mL mol-1). This trend was also observed with the effectors L35 and inositol hexakisphosphate (IHP), and in phosphate buffers. L35 , IHP, and various buffers were observed to affect the magnitude of enthalpy and volume changes, and to increase the quantum yield for bimolecular rebinding of oxygen.

Time-resolved thermodynamics and transient kinetics for oxygen photorelease from hemoglobin:effector complexes

245th National Meeting (2013)

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