STOCKHOLM — 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. This traffic control system keeps activities inside cells from descending into chaos and has helped researchers gain a better understanding of a range of diseases including diabetes and disorders affecting the immune system, the committee said. Working in the 1970s, '80s and '90s, the three researchers made groundbreaking discoveries about how tiny bubbles called vesicles act as cargo carriers inside cells.