Which German-British biochemist shared the 1945 Nobel Prize with Fleming?

The German-British biochemist who shared the 1945 Nobel Prize with Fleming was Ernst Chain.

Chain was born in Berlin in 1906 and moved to Britain after the rise of Nazism. At Oxford, working with Howard Florey and colleagues including Norman Heatley and Edward Abraham, he helped extract, purify, stabilize, and test penicillin. Fleming had discovered penicillin's antibacterial action in 1928, but Chain's biochemical work helped turn that observation into a usable medicine.

The 1945 Nobel Prize in Physiology or Medicine was awarded jointly to Fleming, Chain, and Florey “for the discovery of penicillin and its curative effect in various infectious diseases.” A common mix-up is to credit Fleming alone with the finished drug: his discovery was the essential starting point, while the Oxford team developed its therapeutic potential. Chain is also easily confused with Florey, who led the Oxford research program and shared the prize.