Structural changes and inhibition of sucrase after binding of scopolamine

Scopolamine (hyoscine) is commonly used as an anticholinergic drug to relieve nausea, vomiting and dizziness of a motion sickness as well as recovery from anesthesia and surgery. Sucrase as a hydrolytic enzyme breaks down sucrose into its monomers, glucose and fructose. The aim of this study was to evaluate the effect of scopolamine on the activity and the structural changes of yeast sucrase. The results showed that binding of scopolamine to sucrase could inhibit the enzyme activity. A non-competitive inhibition was observed in different concentrations of scopolamine (0.6 to 3.6 mM). The study by circular dichroism measurement in far-UV showed that the absolute enzyme exhibited a flat negative trough, indicating the presence of α-helices and β-sheet structures in the enzyme. Binding of the inhibitor on the enzyme made a deeper trough at 218 nm, suggesting the increasing of β-sheet content of the enzyme. Fluorescence measurement showed that binding of scopolamine to free enzyme and enzyme–substrate complex increased the peak intensity at 350 nm and also induced red shift. Our findings suggest that scopolamine binds to the location other than the active site of enzyme and that the binding causes structural changes and inhibits the enzyme activity.