The purpose of this study is to summarize the current knowledge of the enzymes which are involved in the hydrolysis of cyanide, i.e., cyanide hydratases (CHTs; EC 4.2.1.66) and cyanide dihydratases (CynD; EC 3.5.5.1). CHTs are probably exclusively produced by filamentous fungi and widely occur in these organisms; in contrast, CynDs were only found in a few bacterial genera. CHTs differ from CynDs in their reaction products (formamide vs. formic acid and ammonia, respectively). Several CHTs were also found to transform nitriles but with lower relative activities compared to HCN. Mutants of CynDs and CHTs were constructed to study the structure-activity relationships in these enzymes or to improve their catalytic properties. The effect of the C-terminal part of the protein on the enzyme activity was determined by constructing the corresponding deletion mutants. CynDs are less active at alkaline pH than CHTs. To improve its bioremediation potential, CynD from Bacillus pumilus was engineered by directed evolution combined with site-directed mutagenesis, and its operation at pH 10 was thus enabled. Some of the enzymes have been tested for their potential to eliminate cyanide from cyanide-containing wastewaters. CynDs were also used to construct cyanide biosensors.

Laboratory of Biotransformation Institute of Microbiology Academy of Sciences of the Czech Republic Vídeňská 1083 CZ 142 20 Prague Czech Republic

Laboratory of Biotransformation Institute of Microbiology Academy of Sciences of the Czech Republic Vídeňská 1083 CZ 142 20 Prague Czech Republic Department of Biochemistry and Microbiology University of Chemistry and Technology Technická 3 CZ 166 28 Prague Czech Republic

Laboratory of Biotransformation Institute of Microbiology Academy of Sciences of the Czech Republic Vídeňská 1083 CZ 142 20 Prague Czech Republic Department of Biochemistry Charles University Prague Hlavova 8 CZ 128 40 Prague Czech Republic

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