Cd. Borman et al., MECHANISTIC STUDIES ON THE SINGLE COPPER TYROSYL-RADICAL CONTAINING ENZYME GALACTOSE-OXIDASE, Pure and applied chemistry, 70(4), 1998, pp. 897-902
Studies on the single Cu protein galactose oxidase (63kDa; 639 amino a
cids) from Fusarium NRRL 2903 are described. The Cu is coordinated in
a square based pyramid by Tyr-272, Tyr-495 (axial), His-496, His-581 a
nd H2O (the substrate binding site), and the enzyme functions as a 2-e
quivalent oxidase, O-2 --> H2O2, with oxidation of primary alcohol sub
strates RCH2OH to RCHO. The active enzyme has a coordinated tyrosyl (T
yr) free radical at Tyr-272, and along with the Cu-II to Cu-I redox ch
ange gives the required two- equivalent redox capacity. The three oxid
ation states are here written as GOase(ox) (Cu-II, Tyr), GOase(semi) (
Cu-II, Tyr), and GOase(red) (Cu-I, Tyr). Protonation of Tyr-495 is an
important part of the enzymic reaction. Studies described are consiste
nt with a mechanism involving H-atom transfer from substrate RCH2OH to
Tyr at Tyr-272.