Non-Coupled Binuclear Cu Sites

The non-coupled binuclear copper enzymes include dopamine p-monooxy-genase (DpM) and peptidylglycine a-hydroxylating monooxygenase (PHM). Both enzymes catalyze substrate C-H bond hydroxylation (at a Gly backbone C-H bond in PHM and a dopamine benzylic C-H bond in DpM), and kinetic and mechanistic studies have shown that the reaction mechanisms for both DpM and PHM are very similar [14]. The active site structure from the crystal structures of PHM indicates 

The non-coupled nature of the PHM and DpM eopper aetive sites is strongly related to their eatalytie funetion. The reaetion eoordinate generated using DFT [21] suggests that the H-atom abstraetion reaction in PHM and DpM involves a mononuclear CuM(II)-superoxo species via an almost thermoneutral process with a low reaction barrier of 15 kcal/mole, in contrast to the previously believed Cum(11)-OOH intermediate [95], which involves a much higher activation barrier of 37 kcal/mole. The reaction coordinate involving the CuM(II)-superoxo species is supported by recent kinetic studies on DpM [96]. 

Due to the small exchange coupling J, the electronic coupling matrix element Hda contribution to the electron transfer rate is also small (k j- oc -2J [97- 

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