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n.d.e

n.d.e

acyt f and P700+ are redox partners for all the plastocyanins. Plastocyanins from bacteria are also able to bind cytochrome oxidase.

BWhen cytochrome c551 is the donor, a nitrite reductase is the acceptor, whereas cytochrome oxidase is the acceptor when AADH is the donor.

cCu-NIR (blue) is the nitrite reductase interacting with azurins in Achromobacter xylosoxidans, whereas the heme-containing cytochrome cd1 binds to all the other azurins listed. dNot determined.

ePseudoazurins bind to Cu- and heme-containing NIRs and probably also to deaminases and c-type cytochromes in methylotrophic bacteria. ■'This structure was kindly provided by Dr. M. Ubbink.

acyt f and P700+ are redox partners for all the plastocyanins. Plastocyanins from bacteria are also able to bind cytochrome oxidase.

BWhen cytochrome c551 is the donor, a nitrite reductase is the acceptor, whereas cytochrome oxidase is the acceptor when AADH is the donor.

cCu-NIR (blue) is the nitrite reductase interacting with azurins in Achromobacter xylosoxidans, whereas the heme-containing cytochrome cd1 binds to all the other azurins listed. dNot determined.

ePseudoazurins bind to Cu- and heme-containing NIRs and probably also to deaminases and c-type cytochromes in methylotrophic bacteria. ■'This structure was kindly provided by Dr. M. Ubbink.

Fig. 1. Ribbon structure representation of a blue copper protein (spinach plastocyanin) showing the location of the Cu site, also known as the "northern" site, and the "eastern" site. The Cu atom and the side chains of the Cu-ligand residues are shown in sphere and stick representations, respectively.

Fig. 1. Ribbon structure representation of a blue copper protein (spinach plastocyanin) showing the location of the Cu site, also known as the "northern" site, and the "eastern" site. The Cu atom and the side chains of the Cu-ligand residues are shown in sphere and stick representations, respectively.

experimental evidence shows that the type I copper proteins can participate in electron-transfer reactions with different redox proteins (23).

The overall electron-transfer process between a cupredoxin and one of its partners can be written simply as follows:

where the cupredoxin can be either A or B, depending on its redox state and the protein with which it is interacting, and k2 is the kinetic constant for the overall electron transfer reaction (24). However, the molecular mechanism of this reaction is quite complex and the details have not yet been elucidated exhaustively. The overall process is commonly thought to consist of different successive steps: (1) the formation of the complex between the two redox partners, which is necessary to bring the proteins into contact, (2) the electron transfer itself, and (3) the dissociation of the complex after the redox reaction has taken place. These steps can be summarized as follows:

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