CHEMICAL BROMINATION OF PHENOL RED BY HYDROGEN-PEROXIDE IS POSSIBLE IN THE ABSENCE OF HALOPEROXIDASES

The dye phenol red (phenolsulphonphthalein) was chemically brominated to bromophenol blue (3',3 '',5',5 ''-tetrabromophenolsulphonphthalein) directly by hydrogen peroxide (20 mM or higher) under acidic pH (0.5- 4.5) and moderate temperature (30 degrees C). Since this bromination r eaction takes place in the absence of any chemical or biological catal yst, the results represent an important warning concerning a commonly used assay for detecting or screening haloperoxidases. Bromophenol red (5',5 ''-dibromophenolsulphonphthalein) and another unidentified comp ound were observed as temporary intermediates. Incubation of the react ion mixture with KCl instead of NaBr did not yield any chlorinated pro ducts under the same conditions.. (C) 1998 Elsevier Science Ltd.