ic301272h_si_002.pdf (32.6 MB)
Active Site Models for the CuA Site of Peptidylglycine α‑Hydroxylating Monooxygenase and Dopamine β‑Monooxygenase
journal contribution
posted on 2012-09-03, 00:00 authored by Atsushi Kunishita, Mehmed
Z. Ertem, Yuri Okubo, Tetsuro Tano, Hideki Sugimoto, Kei Ohkubo, Nobutaka Fujieda, Shunichi Fukuzumi, Christopher J. Cramer, Shinobu ItohA mononuclear copper(II) superoxo species has been invoked
as the
key reactive intermediate in aliphatic substrate hydroxylation by
copper monooxygenases such as peptidylglycine α-hydroxylating
monooxygenase (PHM), dopamine β-monooxygenase (DβM), and
tyramine β-monooxygenase (TβM). We have recently developed
a mononuclear copper(II) end-on superoxo complex using a N-[2-(2-pyridyl)ethyl]-1,5-diazacyclooctane tridentate ligand, the
structure of which is similar to the four-coordinate distorted tetrahedral geometry of the copper-dioxygen adduct found
in the oxy-form of PHM (Prigge, S. T.; Eipper, B. A.; Mains, R. E.;
Amzel, L. M. Science 2004, 304, 864–867). In this study, structures and physicochemical
properties as well as reactivity of the copper(I) and copper(II) complexes
supported by a series of tridentate ligands having the same N-[2-(2-pyridyl)ethyl]-1,5-diazacyclooctane framework have
been examined in detail to shed light on the chemistry dictated in
the active sites of mononuclear copper monooxygenases. The ligand
exhibits unique feature to stabilize the copper(I) complexes in a
T-shape geometry and the copper(II) complexes in a distorted tetrahedral
geometry. Low temperature oxygenation of the copper(I) complexes generated
the mononuclear copper(II) end-on superoxo complexes, the structure
and spin state of which have been further characterized by density
functional theory (DFT) calculations. Detailed kinetic analysis on
the O2-adduct formation reaction gave the kinetic and thermodynamic
parameters providing mechanistic insights into the association and
dissociation processes of O2 to the copper complexes. The
copper(II) end-on superoxo complex thus generated gradually decomposed
to induce aliphatic ligand hydroxylation. Kinetic and DFT studies
on the decomposition reaction have suggested that C–H bond
abstraction occurs unimolecularly from the superoxo complex with subsequent
rebound of the copper hydroperoxo species to generate the oxygenated
product. The present results have indicated that a superoxo species
having a four-coordinate distorted tetrahedral geometry
could be reactive enough to induce the direct C–H bond activation
of aliphatic substrates in the enzymatic systems.