The School of Molecular and Cellular Biology at the University of Illinois at Urbana-Champaign

Biological Halogenation and Epoxidation Reactions - Peroxidase and Catalase Biochemistry. Chloroperoxidase, an enzyme which catalyzes both epoxidation and halogenation reactions was discovered, crystallized, and characterized in these labs. We have studied the heme active site of this enzyme using various spectroscopic techniques, including Mossbauer, EPR, Raman, MCD, ENDOR, and optical absorption spectroscopy. These investigations all show a close identity of the active site of chloroperoxidase with the cytochrome P-450 family of enzymes. The 3-D X-ray crystal structure of chloroperoxidase has been recently determined by the Poulos labs. Investigations have shown that Compound I, the peroxidase intermediate which is important in halogenation and epoxidation reactions, can be characterized chemically as an oxyferryl pi cation radical. Current studies are threefold. One is aimed at chemically defining the halogenating and epoxidizing intermediates which are formed in the reaction. The chloroperoxidase operon (promoter, signal sequences and structural gene) have been cloned. Thus a second study involves structure -function relationships at the active site of this enzyme. We are carrying out active site and "directed evolution" mutagenesis in order to extend the stereo and regiospecificity for enzymatic halogenation and epoxidation reactions. Chloroperoxidase shows great promise as a chiral catalyst for stereoselective drug synthesis.

Biosynthesis of Methyl Cloride and Related Halohydrocarbons. The most abundant halo-hydrocarbon in the upper atmosphere is methyl chloride. The annual global emission rate of this compound is estimated to be 2x10⁷ tons per year. Prior studies have shown that biosynthetic reactions, not industrial pollution, are the primary source of atmospheric methyl chloride. We have examined fungal, plant and marine sources for the enzymes involved in methyl chloride biosynthesis. To date we have partially purified methyl transferases from wood-rot fungi, marine red algae and the terresterial succulent, ice plant, which catalyze the synthesis of methyl halides from S-adenosyl methionine and either chloride, bromide or iodide. The methyl transferase gene has been cloned and expressed in E. coli. An immediate objective is to transform plants [with the methylase gene to test if they are converted] to higher levels of salt tolerance. A more distant objective involves exploring the potential use of this gene for soil desalinization.