Summary: Bromoperoxidase from Corallina officinalis is a phenoxazine dye. The brilliant cresyl blue (BCB) test determines the activity of glucose-6-phosphate dehydrogenase (G6PDH). The activity of this enzyme is greatest in growing oocytes and declines as oocytes mature. It stains reticulocytes and trichomonads. Bromoperoxidase contains a significant amount of nonheme iron. It is activated by vanadate ions. Maximal activity is achieved with stoichiometric vanadium incorporation.