improved operational stability of chloroperoxidase through use of antioxidants chloroperoxidase cpo from caldariomyces fumago is a potentially very useful enzyme due to its ability to catalyze a large variety of stereoselective oxidation reactions but poor operational stability is a main limitation for commercial use in the present study the possibility of increasing the operational stability by use of antioxidants was investigated using the oxidation of indole as model reaction caffeic acid was the antioxidant showing the strongest positive effects reaching a total turnover number ttn of 135000 at ph 4 and 4 mm hydrogen peroxide compared to 28700 in the absence of antioxidant portionwise addition of hydrogen peroxide in the presence of caffeic acid caused a further increase in ttn to 171000 an alternative way to reach high ttn was to use tertbutyl hydroperoxide as oxidant instead of hydrogen peroxide a ttn of 600000 was achieved although the reaction was quite slow in this case antioxidants did not have any positive effect possible mechanisms for the observed inactivation of cpo are discussed