"Let's face it, aging isn't the same in humans and yeast," said Jef Boeke, a yeast geneticist at the Johns Hopkins University School of Medicine. Besides, he said, sirtuins are potent molecules, and in cranking them up, "one would have to be very careful about potential side effects." The new study caps a three-year string of discoveries involving sirtuins (pronounced sir-TOO-ins), a class of enzymes that are found in virtually every organism, including bacteria, plants and people. As with all enzymes, their job is to promote essential biochemical reactions inside cells.

For years researchers have known that life span can be extended by 50 percent or more in many kinds of creatures, including flies, worms and mice, if the animal is fed a diet that is nutritious but contains about 30 percent fewer calories than usual. Recently scientists found that the life-extending benefits of calorie restriction do not occur if the animal has been genetically altered to lack sirtuins, indicating these enzymes are crucial to this process.

"We're very keen on the idea that this is it" -- that sirtuins are the central regulator of the aging process -- [Leonard Guarente] said. He is a founder of Elixir Pharmaceuticals of Cambridge, Mass., which, like [David Sinclair] and BIOMOL, hopes to capitalize on chemicals that can boost sirtuin activity.