Thioarginine (hydrobromide) is a colorimetric substrate for arginase that provides the basis for continuous spectrophotometric measurement of enzyme activity.{9082} It exhibits Km and kcat values of 0.5 mM and 18,000 min?1, respectively, which are similar to physiological substrate arginine.{9082} The thiol product of the reaction reacts with DTNB to produce 2-nitro-5-thiobenzoate for easy visualization at 405-420 nm.