Enzymatic epoxidation reactions

The oxygenases - enzymes which incorporate molecular oxygen directly into organic molecules - are ubiquitous and of high metabolic significance. These enzymes play crucial roles in the degradation of drugs and foreign substances and in the biosynthesis, interconversion and degradation of amino acids, lipids, porphyrins, vitamins and hormones. Thus, they are centrally involved in the mechanisms of cytotoxicity, mutagenicity, carcinogenicity and tissue necrosis. From the standpoint of enzyme technology, the ability of these enzymes to incorporate molecular oxygen into organic substrates efficiently and selectively is highly enticing, since such reactions are poorly accomplished using conventional chemistry. This review focuses on enzymatic epoxidation reactions, one example of the many chemical transformations catalysed by oxygenases. By way of introduction, an overview of the role of enzymatic epoxidation reactions in the metabolism of polycyclic aromatic hydrocarbons, in steroid biosynthesis and interconversion, and in various other pathways is presented. Following this, enzymatic epoxidation of simple olefins is considered in detail, with emphasis on bacterial systems and discussion of both enzymology and reactivity characteristics. Finally, a number of major issues which must be confronted if complex oxygenase systems are to be utilized in enzyme technology application are briefly discussed. Among these are specialized immobilization techniques, cofactor recycling, problems of enzyme stability, and the intriguing possibility of utilizing mechanistic information in the design of non-enzymatic, chemical model systems which mimic oxygenase catalysis.