NEW YORK — Two Americans shared this year’s Nobel Prize in chemistry for deciphering the communication system that the human body uses to sense the outside world and send messages to cells — for example, speeding the heart when danger approaches. The understanding is aiding the development of new drugs.
The winners, Dr. Robert J. Lefkowitz, 69, a professor at the Duke University Medical Center in Durham, N.C., and a Howard Hughes Medical Institute researcher, and Dr. Brian K. Kobilka, 57, a professor at the Stanford University School of Medicine in California, will split $1.2 million.
Lefkowitz spoke by telephone during the news conference Wednesday at the Royal Swedish Academy of Sciences in Stockholm, which awards the Nobels, and said he did not hear the ringing of the early morning phone call to tell him that he had won.
Lefkowitz and Kobilka filled in a major gap in the understanding how cells work and respond to outside signals.
“It’s a great tribute to human ingenuity and helping us learn intricate details of what goes on in our bodies,’’ said Bassam Shakhashiri, president of the American Chemical Society.
Scientists already knew that stress hormones like adrenaline trigger the body’s fight-or-flight reflex — focusing vision, quickening breathing, diverting blood away from less urgent body systems like the digestive tract — but adrenaline never enters the cells.
‘‘A receptor was correctly assumed to be involved,’’ said Sven Lidin, a member of the Nobel Prize committee for chemistry during a news conference Wednesday, ‘‘but the nature of this receptor and how it reacted remained a mystery for a long time.’’
Lefkowitz said although the notion of cell receptors goes back more than a century, ‘‘when I kind of started my work in the area in the early ‘70s, there was still a lot of skepticism as to whether there really was such a thing.’’
By attaching radioactive iodine to a hormone, Lefkowitz was able to track the movement of the hormone and explore the behavior of these receptors. Over the years, he was able to pull out the receptor proteins and show they were specific molecules.
In the 1980s, his group, which included Kobilka as a postdoctoral researcher, searched for and found the gene that produced one of these protein receptors. The genetic blueprint indicated that the shape of the protein included long spirals that wove through the cell membrane seven times. Meanwhile, other researchers had discovered a class of proteins, called G proteins, inside the cell that, when activated, set off a Rube Goldberg cascade of molecular machinery.
The receptor was the last missing piece.