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in basic aqueous media as a model for the biogenesis of the cofactor TPQ is
chemically unfavorable. Upon treatment of 4-alkylcatechol to aqueous base,
hydroxyquinone is generated but with variable yield, while starting with
o-
quinone the yield of hydroxyquinone is lower than that starting with catechol.
This indicates that the reaction sequence proposed for biogenesis of TPQ
cofactor of copper amine oxidase is not applicable in this simple chemical
system. The catalase effect is shown to imply the involvement of in the
transformation of catechol to hydroxyquinone under model conditions. In
addition, no corresponding triol is observed when
-quinone is treated with
aqueous base anaerobically with or without added Cu(II), which indicates that
conjugate addition of water to
o
-quinone does not occur under this solution
chemistry condition. The authors rationalize that the enzyme performs the
conjugate addition of water to
o
-quinone yielding hydroxyquinone TPQ by
taking advantage of tri-histidine-bound copper(II) ion in the active site with
o
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