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Cell. 1995 May 5;81(3):369-77.

The anatomy of a bifunctional enzyme: structural basis for reduction of oxygen to water and synthesis of nitric oxide by cytochrome cd1.

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Laboratory of Molecular Biophysics, University of Oxford, England.


Cytochrome cd1-nitrite reductase is a bifunctional enzyme that catalyzes the one-electron reduction of nitrite to nitric oxide and the four-electron reduction of oxygen to water. The 1.55 A crystal structure of the dimeric enzyme from Thiosphaera pantotropha is reported here. The protein was sequenced from the X-ray structure. Each subunit contains a covalent c heme with two axial His ligands (His-17, His-69) and a unique noncovalent d1 heme ligated by Tyr-25 and His-200. The d1 heme is the mononuclear iron center where both oxygen and nitrite reduction take place. The two types of heme are located in separate domains whose arrangement suggests a mechanism requiring domain movement during catalysis.

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