Professor Sir Peter Ratcliffe, who has been co-awarded the 2019 Nobel Prize in medicine, says it is the 'greatest honour' to be recognised for his work on how cells measure oxygen levels, and that he's already 'had a couple of Champagne receptions'. Americans William Kaelin and Gregg Semenza, and Britain's Peter Ratcliffe, split the nine million Swedish kronor ($914,000, 833,000 euros) award.