Pseudoazurin function

Amicyanin (Husain and Davidson, 1986 Groeneveld etal., 1988) spectroscopically resembles plastocyanin more than pseudoazurin and has about the same number of amino acids, so that its classiflcation has been changed from subgroup II to III (the plastocyanin group see Table II). However, its sequence is distinctly different than the plastocyanins, and the new function may indicate yet another class. 

Blue copper proteins, 36 323, 377-378, see also Azurin Plastocyanin active site protonations, 36 396-398 charge, 36 398-401 classification, 36 378-379 comparison with rubredoxin, 36 404 coordinated amino acid spacing, 36 399 cucumber basic protein, 36 390 electron transfer routes, 36 403-404 electron transport, 36 378 EXAFS studies, 36 390-391 functional role, 36 382-383 occurrence, 36 379-382 properties, 36 380 pseudoazurin, 36 389-390 reduction potentials, 36 393-396 self-exchange rate constants, 36 401-403 UV-VIS spectra, 36 391-393 Blue species... 

Surprisingly, its biological redox partners remain largely unknown. It has been implicated in anaerobic nitrite respiration and it has been shown that azurin can donate electrons to nitrite reductase, a function that is proposed to be carried out by another cupredoxin, pseudoazurin (see Section IV, E). On the other hand, azurin is not an inducible protein and denitrifying bacteria express azurin constitutively under aerobic conditions. 

Although nitrite reductases do not belong to the cupredoxin family, they are discussed together with pseudoazurin because of their close functional relationships). 

The type I copper sites function as electron transfer centers in the blue copper proteins and in multicopper enzymes, particularly oxidases (33). They are characterized by their intense blue color, their unusually small A values, and their very positive redox potentials (Table II). X-ray crystal structures of several blue copper proteins have been determined, notably plastocyanin (34), azurin (35), cucumber basic blue protein (36), and pseudoazurin (37). The active site structures show marked similarities but also distinct differences (Fig. 8). 

Estrada, E. and Uriarte, E. (2005) Eolding degrees of azurins and pseudoazurins. Implications for structure and function. Comp, Biol, Chem., 29, 345-353. 

Amicyanins function as electron carriers in the respiratory chains of some me-thylotrophic bacteria, e.g., Thiobacillus versutus [92]. They transfer single electrons from methylamine dehydrogenase to a cytochrome c [78] which then transfers the electron to cytochrome c oxidase. Amicyanin from Pseudomonas denitrificans has a molecular mass of 11.6 kD and contains 106 amino acid residues. Amicyanin contains one /J-sheet more than the eight of plastocyanin and pseudoazurin, the result of several additional amino acids at its N-terminus [78] (Fig. 15). Like pseudoazurin, amicyanin is found exclusively in bacteria. 

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