Americans James Rothman and Randy Schekman and German-born researcher Thomas Suedhof won the 2013 Nobel Prize in medicine on Monday for discoveries on how hormones, enzymes and other key substances are transported within cells.

The Nobel committee said their research on "vesicle traffic" -- the transport system of our cells -- helped scientists understand how "cargo is delivered to the right place at the right time" inside cells.

Disturbances to the system can contribute to diabetes and neurological and immunological disorders, the committee said.

Rothman, 62, is a professor at Yale University while Schekman, 64, is at the University of California, Berkeley. Suedhof, 57, joined Stanford University in 2008.

"My first reaction was, "Oh, my God!" said Schekman in a statement released by Berkeley. "That was also my second reaction."

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The university said Schekman's research led to the success of the biotechnology industry. Schekman studied normal and defective yeast to identify the process of vesicle transport, the university said.

The Nobel committee said Schekman discovered a set of genes that were required for vesicle transport, while Rothman revealed how proteins dock with their target membranes like two sides of a zipper. Sudhof found out how vesicles release their cargo with precision.

"These discoveries have had a major impact on our understanding of how cargo is delivered with timing and precision within and outside the cell," the committee said.

Rothman and Schekman won the Albert Lasker Basic Medical Research Award for their research in 2002 -- an award often seen as a precursor of a Nobel Prize.

The medicine prize kicked off this year's Nobel announcements. The awards in physics, chemistry, literature, peace and economics will be announced by other prize juries this week and next. Each prize is worth $1.2 million.

Established by Swedish industrialist Alfred Nobel, the Nobel Prizes have been handed out by award committees in Stockholm and Oslo since 1901. The winners always receive their awards on Dec. 10, the anniversary of Nobel's death in 1896.

Last year's medicine award went to Britain's John Gurdon and Japan's Shinya Yamanaka for their contributions to stem cell science.