Magazine article Science News

Stop-Action Crystallography Tracks Enzymes

Magazine article Science News

Stop-Action Crystallography Tracks Enzymes

Article excerpt

Thanks to those ever-adapting soil bacteria, nature has come up with its own ways to get rid of pollutants (SN: 8/15/92, p. 107; 3/14/92, p. 175). Some microbes, for example, have evolved enzymes that break down chlorinated compounds into less toxic components.

Now a Netherlands research team seeking to understand how these enzymes work and to improve upon nature's cleanup efforts has caught one in the detoxification act.

The investigators manipulated the temperature and acidity of solutions containing crystals of haloalkane dehalogenase from a nitrogen-fixing bacterium, Xanthobacter autotrophicus. This slowed the speed of the reaction typically much faster than a second -between the enzyme and its substrate. This enabled them to use X-ray diffraction to determine the positions of the atoms at different stages of the reaction. Koen H.G. Verschueren and his colleagues at the University of Groningen describe their results in the June 24 NATURE.

The data confirm that the enzyme breaks up the pollutant in two steps, not one, as some researchers have suggested, says Bauke W. Dijkstra, a crystallographer with the group.

The team first placed enzyme crystals in an acidic solution (pH 5) with l,2-dichloroethane, cooling it to 4degreeC. Under those conditions, the chlorinated molecule binds to the enzyme but no reaction occurs. Warming the solution to room temperature, allowed the enzyme to break the bond between one chlorine and a carbon atom of the molecule. …

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