STOCKHOLM (AP) - Americans Robert Lefkowitz and Brian Kobilka won the2012 Nobel Prize in chemistry Wednesday for studies of proteinreceptors that let body cells sense and respond to outside signals. Suchstudies are key for developing better drugs.

The Royal SwedishAcademy of Sciences said the two researchers had made groundbreakingdiscoveries on an important family of receptors, known asG-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.

Lefkowitz,69, is an investigator at the Howard Hughes Medical Institute andprofessor at Duke University Medical Center in Durham, North Carolina.

Kobilka, 57, is a professor at Stanford University School of Medicine in California.

"I'm feeling very, very excited," Lefkowitz told a news conference in Stockholm by phone.

He said he was fast asleep when the Nobel committee called.

"Idid not hear it ... I wear earplugs, so my wife gave me an elbow," hesaid. "And there it was. .... It was a total shock and surprise."

Theacademy said it was long a mystery how cells interact with theirenvironment and adapt to new situations, such as when adrenalinincreases blood pressure and makes the heart beat faster.

Scientists suspected that cell surfaces had some some type of receptor for hormones.

Usingradioactivity, Lefkowitz managed to unveil receptors including thereceptor for adrenalin, and started to understand how it works.

Kobilka'swork helped researchers realize that there is a whole family ofreceptors that look alike - a family that is now calledG-protein-coupled receptors.

The Nobel week started Monday withthe medicine prize going to stem cell pioneers John Gurdon of Britainand Japan's Shinya Yamanaka. Frenchman Serge Haroche and American DavidWineland won the physics prize Tuesday for work on quantum particles.

TheNobel Prizes were established in the will of 19th century Swedishindustrialist Alfred Nobel, the inventor of dynamite. Each award isworth 8 million kronor, or about $1.2 million. The awards are alwayshanded out on Dec. 10, the anniversary of Nobel's death in 1896.

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