Amylase substrate based on fluorescence energy transfer

Abstract

A fluorigenic substrate for measuring α-amylase (E.C. 3.2.1.1) activity was prepared by double labeling soluble starch with 5-(4,6-dichlorotrizain-2-yl)aminofluorescein and Procion Red MX8B. Because the absorption spectrum of Procion Red MX8B overlaps the fluorescein emission spectrum, Procion Red efficiently quenches fluorescein emission when it is closer than the critical radius for fluorescence energy transfer. When amylase catalyzes cleavage of a starch molecule between a fluorescein and a Procion Red MX8B, the distance between the two labels increases and the degree of quenching decreases. The rate at which the fluorescence intensity increases is proportional to amylase activity. To maximize the sensitivity it is critical to maximize the amount of Procion Red MX 8B coupled to the starch and to use a high-precision spectrofluorimeter which can measure a small rate of increase in fluorescence above a large constant background.