Shear deformation effects in enzyme catalysis. Metal ion effect in the shear inactivation of urease

The mechanism of the inactivation of the enzyme urease produced by subjecting its dilute solutions to hydrodynamic shear stresses in the range 0.5-2.5 Pa has been determined. By studying the kinetics of urease-catalyzed urea hydrolysis during application of hydrodynamic shear under varying chemical environments, we demonstrate that micromolar quantities of metal ions, in this case adventitious Fe, can accelerate the oxidation of thiol groups on urease and thus inactivate it when the protein is subjected to a shearing stress of order 1.0 Pa. In the absence of metal ion this stress level is ineffectual. It is proposed that this type of synergy between deformation and chemical environment may be crucial in many situations where biological macromolecules are subjected to mechanical stress.