American John B. Fenn, 85, of the Virginia Commonwealth University in Richmond, Koichi Tanaka, 43, of Shimadzu Corp. in Kyoto, Japan, will share one half of the 10 million kronor ($1 million) prize.
Kurt Wuethrich, 64, of the Swiss Federal Institute of Technology in Zurich and the Scripps Research Institute in San Diego, California, will get the other half.
"My wife called me and said 'Come here, get on the phone, it's Stockholm!'" Fenn told CBS Radio News. "It brings an automatic response of ... you knew what it was before you actually heard it, although you can't believe it."
"It's just like being struck by lightning, you know, the odds are so infinitesimal that you never really think you have a chance, so I'm still in a state of shock," he laughed.
They were cited for "the development of methods for identification and structure analyses of biological macromolecules," including proteins.
The laureates' research in two favorite methods among chemists — mass spectrometry and nuclear magnetic resonance — has "meant a revolutionary breakthrough, making chemical biology into the 'big science of our time,'" the Royal Swedish Academy of Sciences said in its citation.
Using the research, chemists can now quickly and reliably identify proteins and can produce three-dimensional images of protein molecules in solutions, leading to a better understanding of how proteins function in cells, the academy said.
The research has led to new drugs and promising applications in the early diagnosis of ovarian, breast and prostate cancer and malaria.
"Mass spectrometry is now beginning to be used to tell the presence of cancer very early on," Fenn said. "That's an art that is still in its very early stages, but the possibility is there."
"All therapeutic strategies today are based on targeting proteins," Bengt Norden, the chairman of the awards committee, said. Methods developed by the laureates "will help us design drug molecules that bind to both proteins and nucleic acids," he added.
Previously only fairly small molecules could be identified, but Fenn and Tanaka developed methods that made it possible to analyze larger molecules as well.
Wuethrich's research in the beginning of the 1980s made it possible to study proteins in solutions, providing an environment similar to that in the living cell.
Reached in Zurich, Wuethrich said he was "delighted and surprised" at being awarded the prize.
"I am glad that such a prize is coming to Switzerland," he told The Associated Press. "At a time when so much seems to be going wrong, this shows that certain things also have gone right."
The Nobel science awards were culminating later Wednesday with the announcement of the economics prize, the only one not established in the will of Swedish industrialist Alfred Nobel, the inventor of dynamite.
The winner of the Nobel Prize in literature was to be named on Thursday in Stockholm and the Nobel Peace Prize on Friday in Oslo, Norway.
The prizes for medicine and physics were announced earlier this week.
For the second year in a row, the academy will award the chemistry and physics honors separately. The academy changed its years-long practice of announcing them the same day after determining that pairing the awards made it too easy for one to be overlooked.
Last year's chemistry award was shared by William S. Knowles and K. Barry Sharpless of the United States and Ryoji Noyori of Japan for discoveries now used to manufacture a wide variety of medicines, including antibiotics, heart drugs and a popular treatment for Parkinson's disease.
The medicine, physics, chemistry, literature and peace prizes were first awarded in 1901. The Nobel Memorial Prize in Economic Sciences was established separately in 1968 by the Swedish central bank, but it is grouped with the other awards.
Nobel gave little guidance other than to say the chemistry prize should go to those who "shall have conferred the greatest benefit on mankind" and "shall have made the most important chemical discovery or improvement."
The prizes are presented to the winners on Dec. 10, the anniversary of Nobel's death in 1896.