X-ray Absorption Spectra of the Oxidized and Reduced Forms of C112D Azurin from Pseudomonas aeruginosa.

The oxidized and reduced forms of a mutant of Pseudomonas aeruginosa azurin, in which the Cys112 has been replaced by an aspartate, have been studied by X-ray absorption spectroscopy. It is well established that the characteristic approximately 600 nm absorption feature of blue copper proteins is due to the S(Cys112) 3ppi --> Cu 3d(x)()()2(-)(y)()()2 charge-transfer transition. While other mutagenesis studies have involved the creation of an artificial blue copper site, the present work involves a mutant in which the native blue copper site has been destroyed, thus serving as a direct probe of the importance of the copper-thiolate bond to the spectroscopy, active site structure, and electron-transfer function of azurin.