International travelers are often advised to eat fresh garlic, as it seems to protect against intestinal ills. Israeli chemists now say they've figured out why: Garlic derails key enzymes needed by parasites and other pathogens to invade cells and to break down food particles.
Garlic is like a binary chemical weapon--it has to be cut or crushed to unleash its antiparasite powers, says chemist David Mirelman of the Weizmann Institute for Science in Rehovot. When that happens, a peptide called alliin comes in contact with an activating enzyme to form allicin, one of garlic's suspected active ingredients. Allicin has been difficult to study biochemically, because, once formed, it quickly reacts with garlic's other components.
Mirelman, chemist Meir Wilchek, and their colleagues got around this problem by developing a method for making pure, semisynthetic allicin. After exposing Entamoeba histolytica parasites to it, the team noted an 80% decrease in the activity of enzymes called cysteine proteinases. Within minutes the parasites were dead, the researchers report in this month's Antimicrobial Agents and Chemotherapy.
The duo has "taken what had been anecdotal reports and provided a rational explanation" for why fresh garlic seems to combat Montezuma's revenge, comments Eric Block, a chemist at the State University of New York, Albany.
Mirelman thinks allicin's powers may transcend the gut. Because cysteine proteases are important in many bacteria and fungi as well as protozoans, garlic "has potential as a very broad spectrum antimicrobial [drug]," he says. Mirelman also speculates that garlic's rumored usefulness against heart disease may come from an ability to interfere with enzymes that synthesize artery-clogging cholesterol.
