STOCKHOLM — Two American researchers won the Nobel Prize in chemistry today for studies of protein receptors that let body cells sense and respond to outside signals like danger or the flavor of food. Such studies are key for developing better drugs.

The Royal Swedish Academy of Sciences said Robert Lefkowitz and Brian Kobilka had made groundbreaking discoveries, mainly in the 1980s, on an important family of receptors, known as G-protein-coupled receptors.

About half of all medications act on these receptors, so learning about them will help scientists to come up with better drugs.

The human body has about 1,000 kinds of such receptors, structures on the surface of cells, which let the body respond to a wide variety of chemical signals, like adrenaline. Some receptors are in the nose, tongue and eyes, and let us sense smells, tastes and light.