The role of His117 in the redox reactions of azurin from Pseudomonas aeruginosa

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Abstract
The electron‐transfer properties of H117G‐ and wild‐type azurin were compared by applying both as electron acceptors in the conversion of 4‐ethylphenol by 4‐ethylphenol methylenehydroxylase (4‐EPMH). The reactivity of H117G‐azurin was determined in the absence and presence of imidazoles, which can substitute the missing fourth ligand. In the absence of imidazoles, H117G‐azurin reacted directly with 4‐ethylphenol, this reaction was abolished in the presence of imidazoles. The enzymatic reduction of H117G‐azurin by 4‐EPMH was 40 times slower than that of wild‐type azurin. The rate of this reaction was enhanced by some imidazoles, diminished by others. In all cases the reduction of H117G‐azurin was irreversible. These results demonstrate that His117 is vital for electron transfer and effectively protects the copper site against aspecific reactions.