BACTERIAL DEHALOGENASES - BIOCHEMISTRY, GENETICS, AND BIOTECHNOLOGICAL APPLICATIONS

This review is a survey of bacterial dehalogenases that catalyze the c leavage of halogen substituents from haloaromatics, haloalkanes, haloa lcohols, and haloalkanoic acids. Concerning the enzymatic cleavage of the carbon-halogen bond, seven mechanisms of dehalogenation are known, namely, reductive, oxygenolytic, hydrolytic, and thiolytic dehalogena tion; intramolecular nucleophilic displacement; dehydrohalogenation; a nd hydration. Spontaneous dehalogenation reactions may occur as a resu lt of chemical decomposition of unstable primary products of an unasso ciated enzyme reaction, and fortuitous dehalogenation can result from the action of broad-specificity enzymes converting halogenated analogs of their natural substrate. Reductive dehalogenation either is cataly zed by a specific dehalogenase or may be mediated by free or enzyme-bo und transition metal cofactors, (porphyrins, corrins). Desulfomonile t iedjei DCB-1 couples energy conservation to a reductive dechlorination reaction. The biochemistry and genetics of oxygenolytic and hydrolyti c haloaromatic dehalogenases are discussed. Concerning the haloalkanes , oxygenases, glutathione S-transferases, halidohydrolases, and dehydr ohalogenases are involved In the dehalogenation of different haloalkan e compounds. The epoxide-forming halohydrin hydrogen halide lyases for m a distinct class of dehalogenases. The dehalogenation of alpha-halos ubstituted alkanoic acids is catalyzed by halidohydrolases, which, acc ording to their substrate and inhibitor specificity and mode of produc t formation are placed into distinct mechanistic groups. beta-Halosubs tituted alkanoic acids are dehalogenated by halidohydrolases acting on the coenzyme A ester of the beta-haloalkanoic acid. Microbial systems offer a versatile potential for biotechnological applications. Becaus e of their enantiomer selectivity, some dehalogenases are used as indu strial biocatalysts for the synthesis of chiral compounds. The applica tion of dehalogenases or bacterial strains in environmental protection technologies is discussed in detail