Copper-dioxygen complexes and their roles in biomimetic oxidation reactions - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 81

physiological conditions, using available oxidants (e.g., dioxygen) or reducing
agents such as glutathione or ascorbic acid (vitamin C).
Protein active-site copper ions perform the functions of electron
transfer (e.g. as electron carriers in photosynthetic organisms or in respiratory
pathways in certain bacteria), 6 reversible and transport, 12 mono- or
dioxygenation of organic substrates [ oxygenases, incorporating one or both
atoms of or oxidation-dehydrogenation of substrates accompanied by
to either hydrogen peroxide or water [ oxidases ]. 12
Comparable functions are carried out by heme and non-heme iron enzymes.
Copper mediated oxidative processes 'gone wrong' have been discussed, 13-15
including in possible connection with aging, “Lou Gehrig's disease” (Cu/Zn
superoxide dismutase mutation), Alzheimer's disease, and others. Separate
copper proteins participate in the biological nitrogen cycle, catalyzing the
reduction of nitrite and nitrous oxide. 16,17 Copper nitrite reductases (i.e.,
possess a active site which binds substrate; this center
receives electrons which are transferred from a nearby 'type 1''blue' copper
center with ligation (Met, methionine). 16 A very recent
protein x-ray structural study reveals a tetranuclear cluster with His ligation
(so called ) as the active site which effects the
conversion, after receiving reducing equivalents passed on by the binuclear
electron-transfer center (with ligation). 18-20
The major classes of copper proteins involved in are
given in Table 1. Some details of the active sites and chemistry of proteins
most relevant to the chemistry described in this article is provided below.

1.2.1 anin, Tyrosinase, and Catechol Oxidase.

Dioxygen transporting hemocyanins occur in the hemolymph of
mollusks and arthropods. Dioxygen binding occurs with a
reaction stoichiometry, formally an oxidative addition reaction, with ligation
in the 'oxy' form occurring in a side-on

Hemoc y

peroxo

fashion, as indicated in Scheme 1. 12,21,22

An x-ray structure is not available for the monooxygenase tyrosinase,
but spectroscopic and biochemical insights reveal its active site to be very
similar to the binuclear site in hemocyanins. 12 The dioxygen-adduct