Stability of glycolytic enzymes of human erythrocytes

The stability of various glycolytic enzymes of human erythrocytes has been studied by the mechanical shaking method. The rate of denaturation apparently followed first order kinetics. The t1/2, the shaking time required to denature 50% of the original activity, for glucose-6-phosphate dehydrogenase, phosphofructokinase, and pyruvate kinase was less than 1 min; that for hexokinase, 6-phosphogluconate dehydrogenase, and monophosphoglyceromutase was between 2 and 13 min; that for all the other enzymes was more than 30 min. Since the t1/2 value for each enzyme is highly reproducible if the shaking conditions are kept constant, these parameters may be used as an indicator of protein stability in solution. The mechanical denaturation method may also be used to remove unstable components from a mixture of proteins with different stabilities.