Axelrod, Julius (1912-2004), an American biochemist, shared the 1970 Nobel Prize in physiology or medicine with Bernard Katz from the United Kingdom and Ulf Svante von Euler from Sweden. The three scientists were honored for their independent studies of neurotransmitters, chemicals that carry nerve impulses from cell to cell. Axelrod studied the role of two enzymes that break down chemical neurotransmitters once they are no longer needed to transmit nerve impulses. An enzyme is a molecule that speeds up chemical reactions in living organisms. See Enzyme.