Cosolvent control of substrate inhibition in cosolvent stimulation of β-glucuronidase activity

Bacterial β-glucuronidase exhibits a considerable increase in specific activity, upon addition of suitable organic cosolvents to aqueous systems. The effect is especially marked with three to five carbon alcohols; a nine fold increase was observed in this study using t-butanol in the range of 10% by volume of t-butanol in water. Most such increases were previously ascribed to cosolvent effects on V max, i.e. to the catalytic steps. However, it is shown here that this enzyme is susceptible to marked substrate inhibition, and that half of the cosolvent induced activity increase is due to decreasing this inhibition. The other 50% of the activity increase probably does reside in cosolvent stimulation of V max.