US chemists Robert Lefkowitz and Brian Kobilka won the Nobel Prize on Wednesday for identifying a class of cell receptor, yielding vital insights into how the body works at the molecular level.

The award is for chemistry but the big beneficiary is medical research, the Nobel committee declared.

The pair were honored for discovering a key component of cells called G-protein-coupled receptors and mapping how they work.

The receptors stud the surface of cells, sensitizing them to light, flavor, smells and body chemicals such as adrenaline and enabling cells to communicate with each other.

About a thousand of these kinds of receptor are known to exist throughout the body. They are essential not just for physiological processes but also for response to drugs.

"About half of all medications achieve their effect through G-protein-coupled receptors," the Nobel jury said.

Understanding the receptors provides the tools for "better drugs with fewer side effects," Nobel committee member Sven Lidin said.

Lefkowitz, 69, is a professor of biomedicine and biochemistry at Duke University in North Carolina, while Kobilka, born in 1955, is a professor of molecular and cellular physiology at Stanford University School of Medicine in California.

In a teleconference with Swedish journalists, Lefkowitz admitted he had not heard the phone ring to get the famous piece of news.

"I was fast asleep and the phone rang. I did not hear it. I must share with you that I wear ear plugs to sleep, and so my wife gave me an elbow: 'phone for you.' And there it was. A total shock and surprise," he said.