A fluorescent probe for the active site of bovine trypsin

The compound 2-p-toluidinylnaphthalene-6-(N-beta-ethylamine hydrochloride) sulfonamide (compound III) has a structure that is appropriate for binding to the active site of trypsin. It also has the property of fluorescence when in a nonpolar environment such as when bound to trypsin. Kinetic studies show that compound III competitively inhibits the trypsin-catalyzed hydrolysis of L-alpha-N-Benzoylarginine-p-nitroanilide (L-BAPNA) with a KI' of 3.6 X 10(-4)M at pH 8.1. The fluorescence enhancement of III when bound to bovine trypsin further confirms the existence of a hydrophobic specificity region within the active site of trypsin. The pH dependence of the fluorescence of compound III with trypsin was also determined.