Chromogenic substrates are routinely used for spectroscopic analysis of enzyme activity1,2. The 5-bromo-4-chloroindol-3-yl group may be a particularly useful group in identifying ribonuclease activity. Specific ribonucleases should cleave the bond between the phos- phate and the chromophore. The oxidation of the resulting 5-bromo-4-chloroindol-3-ol to a dimeric product results3 in an important absorbance increase between 600 and 700 nm. For this reason a ...
