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Results show that copperA-domain of cytochrome oxidase subunit II from Paracoccus denitrificans is Ph responsive exhibiting conformational changes at the copperA site with pH decrease. Data further indicate that the protein's conformational state is more stable at the 'low-pH' and the conformational transition is influenced by a slow deprotonation step.

A unique and enhanced strategy for purifying nitric oxide reductase (NOR) form membranes of Paracoccus denitrificans was developed. The purified enzyme was identified as a cytochrome bc complex which has two subunits in a 1:1 stoichiometry. The purified NorBC complex binds 0.87 g of dodecyl maltoside/g of protein and produces a dimer in solution. The NorB subunit resembles the primary catalytic subunit of cytochrome oxidase and is believed to contain the active bimetallic center in which two NO molecules are passed on to N2O.