6GEP:
reference: Probing the catalytic mechanism of sulfite reductase by X-ray crystallography: structures of the Escherichia coli hemoprotein in complex with substrates, inhibitors, intermediates, and products., Crane BR, Siegel LM, Getzoff ED, Biochemistry 1997 Oct 7;36(40):12120-37. PMID: 9315849

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