Enzymes release caged chemicals.

A new controlled-release system relies on enzymes to unshackle chemicals only when and where they're needed. Scientists at the Netherlands Organization for Applied Scientific Research in Zeist are developing what they're calling bioswitches for a number of applications, such as a germ-killing plastic wrap for meats.

The researchers encapsulated lysozyme-a natural antibiotic--within a cage of chemically linked starch molecules and seeded the complexes onto the wrap's surface. Any bacteria contaminating a piece of meat would view the starch as a snack, explains project manager Hans Boumans, a biochemist. Once the microbe starts feasting on the starch cage, it opens holes and releases the killer lysozymes. "It's like a Trojan horse," says Boumans.

Contact lens cleaners offer another application. Wearers are supposed to soak their dirty lenses for 7 minutes in dilute hydrogen peroxide and then neutralize the chemical with the enzyme catalase. However, impatient consumers often neutralize the solution too soon, cutting short the disinfection step.

The Dutch researchers developed a catalase-releasing bioswitch that can be added to the peroxide at the same time as the lenses are. Boumans' team engineered the bioswitches to release a starch-degrading enzyme--amylase--that slowly breaks apart the cage that contains it. They tweaked the cage design so that it would degrade after only 7 minutes of soaking.

The team is also tailoring edible bioswitches to protect expensive mid unstable flavoring molecules until they contact enzymes on the taste buds, Boumans says. Other complexes would bypass the tongue and carry certain foul-tasting nutrients to the stomach, where enzymes would release the molecules.