Galactose oxidase primary

Copper(II) complexes with phenoxo ligands have attracted great interest, in order to develop basic coordination chemistry for their possible use as models for tyrosinase activity (dimeric complexes) and fungal enzyme galactose oxidase (GO) (monomeric complexes). The latter enzyme catalyzes the two-electron oxidation of primary alcohols with dioxygen to yield aldehyde and... 

Another oxidizing enzyme with very interesting synthetic potential is galactose oxidase [14]. This copper protein oxidizes primary hydroxy functions in polyols enantioselectively to the corresponding aldehydes. Thus, sugar alcohols may be transformed into the interesting non-natural L-configurated... 

Galactose oxidase exhibits a surprisingly low specificity for the primary alcohol but is completely regioselective secondary alcohols are not substrates. This re-gioselectivity suggests potential synthetic applications (117) and has raised interest in the design of small molecule catalysts mimicking GO reactivity. 

These systems are also described as normal copper proteins due to their conventional ESR features. In the oxidized state, their color is light blue (almost undetectable) due to weak d-d transitions of the single Cu ion. The coordination sphere around Cu, which has either square planar or distorted tetrahedral geometry, contains four ligands with N and/or 0 donor atoms [ 12, 22]. Representative examples of proteins with this active site structure (see Fig. 1) and their respective catalytic function include galactose oxidase (1) (oxidation of primary alcohols) [23,24], phenylalanine hydroxylase (hydroxy-lation of aromatic substrates) [25,26], dopamine- 6-hydroxylase (C-Hbond activation of benzylic substrates) [27] and CuZn superoxide dismutase (disproportionation of 02 superoxide anion) [28,29]. 

Nonblue. These include galactose oxidase (GO) and amine oxidases (e.g., plasma amine oxidase, diamine oxidase, lysyl oxidase), which produce dihydrogen peroxide by the two-electron reduction of 02 [33], For GO (stereospecific primary alcohol oxidation), spectroscopic studies by Whittaker [70,71] suggest that the two-electron oxidation carried out by a mononuclear copper center is aided by a stabilized ligand-protein radical (i.e., (L)Cu(I) + 02 —> (L +)Cu(lI) + H202), obviating the need to get to Cu(III) in the catalytic cycle. Protein x-ray structures [33,72] reveal a novel copper protein cofactor, which would seem... 

Galactose oxidase is an extracellular enzyme secreted by the fungus Dactylium den-droides. It is monomeric (M = 68000), contains a single copper site and catalyses the oxidation of a wide range of primary alcohols to the corresponding aldehydes. The two-electron transfer reaction RCH2OH - RCHO + 2H+ + 2e does not utilise a Cu(III)/Cu(I) couple, but a second redox site, involving a tyrosine radical which mediates the transfer of the second electron. 

An example of a one-pot, three-step catalytic cascade is shown in Fig. 1.51 [139]. In the first step galactose oxidase catalyses the selective oxidation of the primary alcohol group of galactose to the corresponding aldehyde. This is fol-... 

Galactose Oxidase (GO) from the filamentous wheat-root fungus Fusarium spp. is a mononuclear type 2 copper enzyme that catalyzes the two-electron oxidation of a large number of primary alcohols to their corresponding aldehydes, coupled with the reduction of dioxygen to hydrogen peroxide [1,18] ... 

As a mimic of the well-studied galactose oxidase [37], a copper(II) thiophenol complex catalyzes the oxidation of primary alcohols to aldehydes in the presence of (Scheme 12) [38]. The latter also promotes the oxidation of secondary alcohols to diols (Scheme 12). The catalytic cycle starts with the oxidation of copper by O, leading to a biradical species. The intermediate 39 is produced from 38 by coordination of two alkoxide substrates. The rate-limiting step is the formation of 40 from 39 by a hydrogen atom transfer from the secondary alcoholate to the oxygen-centered radicals of the aminophenols ligands. The cycle is then closed by radical dimerization which leads the formation of the diol [39]. 

Function. Galactose oxidase catalyses the oxidation of primary alcohols to aldehydes, reducing oxygen to hydrogen peroxide in a two-electron reduction [30] ... 

An example is galactose oxidase which catalyses the oxidation of a primary alcohol to an aldehyde. However, the mechanism of this reaction is not clear although it has been suggested that the active enzyme contains Cu(II) and hydride transfer from the alcohol to the metal (LI) is followed by two 1-electron transfers... 

The selective aerobic oxidation of primary alcohols to aldehydes, but not secondary alcohols to ketones, is reminiscient of the chemistry catalyzed by the Cu-dependent enzyme, galactose oxidase (39). Similarly, the Cu-binding P-amyloid protein relevant to Alzheimer s disease promotes aerobic oxidation of cholesterol, a primary alcohol (cholesterol oxidase activity) (40). The Cu-dependent amine oxidases catalyze the aerobic oxidation of amines to aldehydes (41), the hydration products of imines. Each of these enzymes that promotes aerobic oxidation of primary alcohols and amines to the same products as Ni(TRISOX) catalyze the net reaction in Equation 1. If the net reactions... 

In 1998, a third efficient functional model of galactose oxidase was published by Saint-Aman et aL 86) who performed the electrochemical catalytic oxidation of primary alcohols to the corresponding aldehydes. was obtained from one equivalent Cu C104, 2 equivalents of triethylamine, and one equivalent of the ligand N,N-his (2-hydroxy-3,5-di- cr -butylbenzyl)-... 

Galactose oxidase (54,76,77) is active as a catalyst in two separable reactions, the oxidation of a primary alcohols (reaction (36)) (77) and the reduction of diojgigen to hydrogen peroxide (reaction (37)) (77) ... 

Galactose oxidase (GO) catalyses the two-electron oxidation of primary alcohols to aldehydes. It contains a single type II copper centre. The enzyme employs the metal and a protein radical cofactor to effect the chemistry. The crystal structure shows a square pyramidal five-coordinate copper site with the metal coordinated by two histidines, two tyrosines and a water or acetate ligand. The equatorial tyrosine, Tyr272, has an interesting crosslink to a cysteine group ortho to the tyrosine oxygen. 

---