A caution about the azide inhibition of enzymes associated with electrophilic metabolites

Azide is often used as an inhibitor to detect active site metal ions present in enzymes such as tyrosinases and laccases. Azide is not only a good chelator for metal ions, but also a powerful nucleophile. Consequently, some of the observed inhibition of tyrosinase by azide can be explained by the reaction of enzymatically generated quinones with azide to form azido catechol. In the light of this finding, routine use of inhibition studies with azide to detect the metal ions present at the active site of enzymes generating and/or consuming electrophilic metabolites is discouraged.