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Antibody spurs disfavored reaction.

Baldwin said it shouldn't happen.

According to the catalog of predicted outcomes for ring-forming chemical reactions, also known as "Baldwin's rules," a molecule like trans epoxy-alcohol should not often bend into a contorted chemical creature tipped by a six-atom ring. That requires a lot of strain on the molecule's atomic scaffolding. In the "favored" reaction, such a molecule forms a five-atom ring.

But scientists at the Scripps Research Institute in La Jolla, Calif., performed the disfavored chemical maneuver anyway with the help of a new catalytic antibody. These custom-made molecules, resembling those normally found in animals' immune systems, act like enzymes and other catalysts, throttling up the rate at which a chemical reaction occurs.

Antibodies prowl the body on the lookout for bacteria and other unwanted foreign substances, or antigens. When they meet, the antibody binds to the antigen, marking it for destruction. Inspired by the immune system's creative power, chemists have found ways to harness nature's machinery -- in this case, the immune systems of mice - to manufacture antibodies with a predetermined structure and electrical charge for use as catalysts in chemical reactions.

Since 1986, when scientists first created catalytic antibodies, chemists have pursued ways of using the binding properties of these laboratory-made immune-system molecules to perform diverse chemical tasks, including DNA repair and manufacturing pharmaceuticals with fewer side effects (SN: 9/2/89, p. 152).

In the new research, described in the Jan. 22 SCIENCE, Scripps scientists Kim D. Janda, Charles G. Shevlin, and Richard A. Lerner announce a novel catalytic antibody that speeds the conversion of trans epoxy-alcohol molecules into tetrahydropyrans, chemical building blocks that form important, naturally occurring organic molecules. Brevetoxins, for example, the deadly by-products of a massive algae bloom popularly known as "red tide?' contain tetrahydropyrans, Janda notes.

This is the first catalytic antibody shown to work in a disfavored reaction, Janda emphasizes. And at the moment, it occupies a unique niche in organic chemistry's catalytic bestiary. "There's no [other] enzyme or synthetic catalyst known that can do this," Janda notes.

Chemists can synthesize the disfavored molecules in a laborious, seven-step process. But if simply mixed with the necessary reagents, says Janda, trans epoxyalcohol almost always forms the favored five-atom rings.

The importance of this new catalytic antibody extends beyond its novel ability to spur a disfavored chemical reaction, says organic chemist Samuel Danishefsky of Yale University. The new report, he says, suggests that chemists might, in time, design functionally unique catalytic antibodies rather than ones that simply mimic the properties of known enzymes and synthetic catalysts.

"They have created now a major challenge for themselves?' Danishefsky says of the Scripps researchers. "If they meet that challenge with any degree of consistency. then it will become very important."
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Title Annotation:laboratory-made immune-system catalyst
Author:Pendick, Daniel
Publication:Science News
Date:Jan 30, 1993
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