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On The Track Of Enzymes That Can Break Down Pollutants

Biochemist Brian Fox studies a family of enzymes that metabolize compounds as diverse as nutritionally desirable fats and toxic waste.

The enzymes contain a pair of iron atoms held in the protein backbone by amino acid residues. Fox describes these diiron enzymes as tiny, reactive furnaces that burn oxygen and hydrocarbons in a highly controlled manner. He wants to identify the structural and mechanistic features that account for this remarkable control. In the long-term, Fox plans to use this information to make more useful catalysts by engineering changes in the enzyme”s structure.

Fox”s research receives major support from the National Institutes of Health and National Science Foundation and has won him two prestigious junior faculty awards — the Searle Scholarship and the Shaw Scientist Award. Now the work has earned Fox a 1997 Pound Research Award from the College of Agricultural and Life Sciences.

Since coming to the UW-Madison in 1993, Fox and his coworkers have made rapid progress in characterizing the diiron enzyme core and the amino acid residues essential for effective catalytic action. Working with the Biochemistry Pilot Plant, the scientists have also developed cost-effective methods to produce large amounts of these and other enzymes for use in their studies.

One enzyme Fox studies is toluene monooxygenase. It is one of the few enzymes known to break down toxic contaminants such as benzene, chloroform, trichloroethylene, and other halogenated pollutants. Since several of these cancer-causing compounds have turned up in groundwater, scientists want to arm soil bacteria with the most effective enzyme possible and then use these improved bacteria to attack the pollutants. Fox and his research group at the Enzyme Institute have purified each of the four proteins required to accomplish this feat and have begun to characterize their properties.

In collaboration with scientists at New Jersey-based Envirogen, Inc., Fox has engineered a series of mutated forms of toluene monooxygenase. These forms show dramatic differences in catalytic activity and substrate specificity, and are now being evaluated for their ability to break down specific pollutants.

“The work is a tour de force by any standard,” says biochemist Hector DeLuca. “For such a young team, it”s a truly spectacular achievement.”

Fox”s research group is also working with colleagues Hazel Holden and John Markley to determine the three-dimensional structures of the unaltered enzyme and the new forms to learn how changes in the enzyme”s structure contribute to changes in its function. Fox has found that the relationship between this enzyme”s structure and its function is complex, and developing more effective enzymes will be a tricky business. Still, the potential rewards of success in these efforts are great, so the researchers are eager to continue the work.