ABSTRACT
In both enzymes, the abstraction of hydrogen from the substrate molecule is stereospecific and is effected by the organic cofactor. In GOase this step appears to proceed by hydrogen atom abstraction by the modified Tyr272 free-radical site. However, in CAO the TPQ cofactor activates the amine substrate toward deprotona tion by an active site aspartate base. Reflecting this disparity, the active sites of galactose oxidase and amine oxidases are strikingly different. The GOase active site is nonpolar in character, which favors radical chemistry, and very compact, suggest ing that the catalytic events do not involve large movements in active site residues. By contrast, the CAO active site contains many polar residues, and movement in the TPQ cofactor is an essential feature of catalysis.
