Active site models for galactose oxidase and related enzymes

Redox interaction between a transition-metal ion and a redox active amino acid side chain such as the phenol group of tyrosine in several enzymatic systems has been discovered to play a crucial role in biologically important processes. The tyrosyl radical, which directly coordinates to the copper ion center, has recently been found in the active sites of galactose oxidase (GAO) and glyoxal oxidase (GLO). In this article, model studies on the active site of the enzymes are reviewed by summarizing reported information about the physicochemical properties and the redox functions of the Cu(II) and Zn(II) complexes of the phenolate and phenoxyl radical forms of the cofactor models as well as the organic cofactor models themselves.