The Cytochrome cdi from Pseudomonas aeruginosa

It has long been assumed that azurin is an in vivo electron donor to cytochrome cdj of P. aeruginosa. However, construction of mutants of P. aeruginosa in which one or both of the genes for azurin and cytochrome C551 have been deleted has led to the conclusion that in vivo cytochrome C is essential, but that azurin is ineffective, for the donation of electrons to the nitrite reductase (Vijgenboom et al.. 1997). The discrepaney between in vivo and in vitro observations eould be reconciled if it is the failure of azurin to except electrons from the cytochrome bcj complex, or other donor, that is responsible for its ineffectiveness in vivo. 

As mentioned earlier, the copper containing nitrite reductase is a trimer of identical subunits. In each subunit there is a type 1 copper which acts analogously to the c-type heme in cytochrome cd and thus is the point of entry of electron into the enzyme. The three eatalytic sites have type 2 

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