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.
Azurins and pseudoazurins participate in denitrification processes in bacteria.
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