Azurin is a bacterial blue copper protein found in Pseudomonas, Bordetella, or Alcaligenes bacteria, which undergoes oxidation-reduction between Cu(I) and Cu(II), and transfers single electrons between enzymes associated with the cytochrome chain. The protein has a molecular weight of approximately 16,000, contains a single copper atom, is intensively blue, and has a fluorescence emission band centered at 308 nm.
Azurin and cytochrome c551 are involved in electron transfer during denitrification in P. aeruginosa. Azurin from P aeruginosa is a type I blue copper protein with a molecular mass of 14 kDa, while cytochrome c551 (9 kDa) is a haem-containing cytochrome. Azurin possesses a relatively large hydrophobic patch close to the active site, and two residues in this hydrophobic patch, Met-44 and Met-64, are believed to be involved in its interaction with the redox partners cytochrome c551 and nitrite reductase
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