Enzyme inactivation and stabilization studies in an ultrafiltration reactor

Summary An ultrafiltration membrane enzymatic reactor is used in connection with different reacting systems.The experimental conditions are such that the enzyme, which operates at fairly high concentration levels because of the concentration polarization phenomena taking place in the reactor, is still in soluble form.The analysis of the system unsteady-state response enables the identification of the mechanism of enzyme deactivation and the extraction of the kinetic parameters of both the deactivation and the main reaction.The stabilizing effect observed in connection with enzyme entrapment within an inert gel deposited onto the U.F. membrane active surface is also discussed.List of Symbols A U.F. membrane cross sectional area cm² - C_E Enzyme concentration mg/ml - C_EI Enzyme concentration at the active membrane surface mg/ml - C_E Mean enzyme concentration mg/ml - c _s ^o Substrate concentration in the feed m moles/ml - c _s ^u Substrate concentration in the outlet m moles/ml - D_E Enzyme diffusivity cm²/s - Km michaelis constant mM - k₂ Kinetic constant of the enzymatic reaction m moles/mg s - k_d Kinetic constant of the enzyme deactivation reaction s^–1 - N^o Initial amount of active enzyme mg - N(t) Active enzyme amount at reaction time t mg - Q Flow rate ml/s - r Rate of the main reaction m moles/ml s - t Reaction time s - t^* Reaction time at which product concentration in the outlet is within ± 2% of the steady-state value s - v Fluid velocity cm/s - V Cell volume ml - V_B Volume within which 99% of the enzyme fed is contained at the steady-state ml - V_S Volume within which 99% of the total substrate concentration drop occurs at the steady-state ml - x Distance upstream the membrane measured from the membrane surface cm     

Conformational and functional properties of hemoglobin in water–organic cosolvent mixtures: Effect of ethylene glycol and glycerol on oxygen affinity

We report on the effects that the presence of ethylene glycol or glycerol has on the oxygen affinity of hemoglobin. We attribute these effects to an altered equilibrium between T and R quaternary conformations of hemoglobin and separate them into bulk-electrostatic and non-bulk-electrostatic contributions to the standard free-energy difference between the R and T states.