Stein, William Howard (1911-1980), an American biochemist, shared the 1972 Nobel Prize for chemistry with American scientists Christian B. Anfinsen and Stanford Moore, for their contribution to the chemistry of proteins (see Anfinsen, Christian Boehmer; Moore, Stanford). Stein and his collaborators were the first to discover the complete chemical structure of the enzyme ribonuclease. They also analyzed the structures of amino acids and peptides--both constituents of proteins. See Enzyme; Protein.