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Keywords:

  • biocatalysis;
  • singlet oxygen production;
  • vanadium chloroperoxidase (VCPO)

Abstract

Chemiluminescence studies show that the enzyme vanadium chloroperoxidase from the fungus Curvularia inaequalis is a highly efficient catalyst for the production of singlet oxygen from hydrogen peroxide in a mildly acidic aqueous environment, with a maximum turnover frequency of 100 s−1 with respect to H2O2 consumption. The enzyme studied here can be regarded as a supplementary catalyst to inorganic molybdate, which operates in basic aqueous media. The enzyme system is 103 – 104 times faster than the molybdate system when compared at their optimal pH. The enzyme is very stable against singlet oxygen, in contrast to heme-containing peroxidases which, due to inactivation by singlet oxygen, only produce a short burst, presumably by oxidation of the labile cofactor. The vanadium chloroperoxidase was compared with vanadium bromoperoxidase from the seaweed Ascophyllum nodosum and was found to be even more stable; it is stable towards a continuous flow of singlet oxygen for at least 1 hour and also it is not inactivated by 500 mM H2O2. An important difference with vanadium bromoperoxidase is that the vanadium chloroperoxidase is able to effectively use chloride as a cocatalyst (20 s−1) instead of bromide. This offers an important advantage from an application point of view; using chloride, no side products are observed when the chemical trap anthracene-9,10-bis(ethanesulphonate) is fully converted by singlet oxygen into its corresponding endoperoxide. By contrast, when bromide is used, 20% side product is formed. During the conversion the enzyme remains fully stable for 25,000 turnovers.