6-Aminoquinoline as a fluorogenic leaving group in peptide cleavage reactions: A new fluorogenic substrate for chymotrypsin

A new fluorogenic substrate capable of measuring the amidolytic activity of chymotrypsin and based upon the enzyme-catalyzed release of a highly fluorescent aromatic amine, 6-aminoquinoline, was prepared. The substrate, 6-(N-glutaryl-l-phenylalanylamido)quinoline, was found to have at pH 8.0 and 25°C K_m = 1.77 mm and k_cat = 1.4 × 10^?1 s^?1. The aminoquinoline is a unique leaving group in that its appearance can be measured fluorometrically at its excitation and emission maxima, while, under these conditions, fluorescence associated with unhydrolyzed substrate is negligible.