A bug's kiss has chemistry in humans.

Euphemistically known in tropical climates as the kissing bug, the insect Rhodnius prolixus lives in cracks and crevices but crawls out to suck human blood. As it feeds mosquitolike, the bug dribbles saliva into its victim's tissues. Proteins in the saliva somehow deliver nitric oxide (NO), a molecule that opens up blood vessels and prevents clotting (SN: 10/17/98, p. 246). The effect allows R. prolixus to finish its feast.

Now, a team of researchers from the University of Arizona in Tucson and the University of Amsterdam has found that these proteins, known as nitrophorins, are unique in the way they hold NO in the insect's saliva--and then release it in human tissues.

In South America, the kissing bug is responsible for transmitting Chagas' disease, a parasitic infection that causes heart-muscle damage and sometimes death. Learning about nitrophorins might not shed light on how to prevent this illness, says Arizona chemist F. Ann Walker, but it could have an impact on human health in other ways. Compounds that either soak up or deliver NO could be used as drugs to fight cardiovascular disease or the effects of bacterial infections, for example.

Walker and her colleagues performed several experiments on nitrophorin 1, the most abundant of the kissing bug's four nitrophorins, to explore the way it binds to NO. They found that in the insect, NO binds tightly to an iron atom in nitrophorin 1, but not so tightly that it can't break free once in target tissue, Walker explains. "This is a nice balance. ... You want it to be stable but not too stable." The researchers report their findings in the Jan. 13 Journal of the American Chemical Society.

The researchers predict that nitrophorins can store NO in the kissing bug's acidic saliva for up to one month. In the more neutral environment of a victim's tissues, NO breaks free and diffuses into the tissues.

"It's the only known natural NO storage and transport protein," says Donald E. Champagne of the University of Georgia in Athens, who cloned the gene for nitrophorin 1 in 1994. "These molecules are pretty unique."

Walker and her colleagues are also looking at how nitrophorins corral histamines, itch-inducing compounds released by the body's immune response. Blocking these chemicals facilitates the blood sucking by preventing the victim from noticing the bug until it's done feeding, says Champagne.

"These insects are darned clever," Walker notes. "They'll probably be around long after mammals have left the face of the Earth"--provided, of course, that they find something new to eat.