Phosphorescence from Trp-48 in azurin: Influence of Cu(II), Cu(I), Ag(I), and Cd(II) at the coordination site

The phosphorescence yield and triplet lifetime of Trp-48 in Pseudomonas aeruginosa azurin were studied as a function of temperature from 140 to 300 K. The decay in Cu(II), Cu(I), and apoazurin is strictly monoexponential and the triplet lifetime is practically indistinguishable among the various forms. Given the proximity of protein-bound copper to Trp-48 and the structure-modulating role exhibited by nonquenching Ag+ and Cd2+ ions complexed to apoazurin, the apparent inertness of copper is best accounted for if in azurin samples all the phosphorescence intensity originates from an apolike protein contaminant. © 1991 American Chemical Society.