Environment of the manganese binding site in SOD. One subunit of the homodimeric enzyme is shown, with the active site Mn ion (red) buried in the interior of the protein coordinated by four amino acid side chains (green). Main chain tracing is color coded (yellow, N-terminal; orange, C-terminal), and aromatic amino acids are shown (tyrosine, violet; tryptophan, blue). (Based on Protein Data Bank ID 1VEW).