This EnzChek Protease Assay Kit (red fluorescence) contains a casein derivative that is heavily labeled with the pH-insensitive, red-fluorescent BODIPY TR-X, resulting in almost total quenching of the conjugate's fluorescence. Protease-catalyzed hydrolysis releases highly fluorescent BODIPY TR-X dye—labeled peptides and allows quantitative detection of protease activity in solution.