Azurin Alcaligenes faecalis

The crystal structure of the pseudoazurin from Alcaligenes faecalis S-6 sometimes referred to as the blue protein (also as cupredoxin), has been reported to 2.0 A [74]. The protein folds in /3-sandwich which is described as being similar to plastocyanin and azurin. 

The first crystal structure information on a blue copper protein, for poplar plastocyanin in the Cu(II) state, was published in 1978 (2, 3). Since then, the Cu(I) state and related apo and Hg(II) substituted forms (5, 6), the green algal plastocyanin from Enteromorpha prolifera [Cu(II)] (7), azurin from Alcaligenes denitrificans [Cu(II) and Cu(D] (8, 9), azurin from Pseudomonas aeruginosa [Cu(II)] (10, 11), as well as pseudoazurin from Alcaligenes faecalis S-6 (12), and the cucumber basic protein, both in the Cu(II) state, have been published (13), making this one of the best-documented class of proteins. In addition, information as to three-dimensional structure in solution has been obtained from two-dimensional NMR studies on French bean and Scenedesmus obliquus plastocyanins (14,15). This review is concerned in the main with the active site chemistry. Other recent reviews are listed (16-20). 

C-Terminal Ligand-Containing Loop of Paracoccus uersutus Amicyanin, Poplar Plastocyanin, Alcaligenes faecalis S-6 Pseudoazurin, and Pseudomonas aeruginosa Azurin... 

The inducible arsenite oxidase from the Eubacterium Alcaligenes faecalis (NCIB 8687) has been purified and characterized (22-24). Anderson et al. (24) isolated the enzyme from a sonicate of washed, lysozyme-treated cells that had been harvested in their late exponential growth phase. The sonicate was fractionated by gel filtration through DEAE-sepharose and active fractions concentrated by ultrafiltration. The purified enzyme was found to be monomeric with a molecular mass of 85 kDa. It consisted of two polypeptide chains in an approximate ratio of 70 30. The enzyme stmcture included one molybdenum, five or six iron atoms, and sulfide. Purification of the oxidase also led to recovery of azurin, a blue protein, which was rapidly reduced by arsenite in the presence of catalytic amounts of Aro, and a red protein. The red protein was a c-type cytochrome, which was reduced by arsenite in the presence of catalytic amounts of Aro and azurin. No reduction of the cytochrome occurred in the absence of Aro, but it did occur in the absence of azurin. Denaturation of Aro led to the release of a pterin cofactor characteristic of molybdenum hydroxylases. In intact cells of A. faecalis, the enzyme resides on the outer surface of the inner (plasma) membrane. The cytochrome and azurin may be part of an electron transfer pathway in the periplasm. 

Proteins of this class which have received the most attention were isolated from four bacterial species Pseudomonas aeruginosa, Ps. fluorescens, Ps. denitri-ficans, and Bordetella pertussis, although Sutherland (5) has isolated azurin from several other strains of Pseudomonas, Bordetella, and Alcaligenes. The near identity of azurins isolated from these different sources, has been generally assumed, and with one possible exception, that from Ps. denitrificans which does not bind to carboxy-methyl cellulose resin at the same pH as the other proteins (5), this seems to be the case. Ambler and Brown [6), who have elucidated the amino acid sequence of Ps. fluorescens azurin state that B. bronchiseptica, A. denitrificans and faecalis, Ps. denitrificans and fluorescens yield azurins having homologous amino acid sequences. 

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