Continuous bromination of barbituric acid by chlorperoxidase from pseudomonas pyrrocinia

Several hundred halogenated compounds, such as antibiotics, pesticides etc., are present in nature as intermediates and products of many biosynthetic pathways. The enzymes for halogenation reactions within these pathways are largely unknown. In contrast to chemical halogenation enzymatic halogenation reactions proceed under mild conditions and yield less byproducts than comparable technical reactions. So far, only enzymes from eukaryotes, marine algae and fungi were described all of them whit heme at their catalytic site. Recently bacterial enzymes, bromoperoxidases from Streptomyces and Pseudomonas strains, were detected (1,2,3). Some of these bacterial bromoperoxidases have no peroxidase or catalase activity. These new haloperoxidases contain no heme, and up to the description of the catalytic center were termed non-heme haloperoxidases. Besides bromoperoxidase activity, one of these non-heme enzymes has also chlorinating activity (3,4). A typical problem with heme haloperoxidases is the decrease of halogenating activity within short time periods due to H2O2-consumption in side reactions and irreversible inactivation of the respective enzyme. These properties prevent the technical application of heme enzymes for halogenation reactions. Non-heme haloperoxidases, however, show constant halogenation rates over days under these conditions. They have no H2O2 consuming side activity, and therefore should be useful for technical halogenation reactions. Some of these haloperoxidases were characterized with respect to substrate speepcifity and enzyme reactor performance. Here we report on the continuous bromination of barbituric acid (Fig.1) with immobilized chloroperoxidase (CPO) from Pseudomonas pyrrocinia as a model system