Catalytic Reactions of Radical Enzymes

Publisher Summary This chapter discusses catalytic reactions of radical enzymes. The number of enzymes discovered to harbor and employ a metastable radical site for the catalytic activity has steadily increased over the past decades. Besides “pure” radical enzymes—for example, systems that use a stable radical for the catalytic action at the active site—theoretical studies indicate that radical intermediates are also employed in several other systems. Ribonucleotide reductases (RNR) constitute a large group of essential enzymes with a diverse array of primary as well as quaternary structures. Radical enzymes in particular radical reactions are usually characterized by high turnover for the catalytic processes. It is rather difficult to study these reactions experimentally to gain direct insight into the mechanisms. For the Cu-containing system Galactose oxidase, the chapter concludes that the unpaired spins initially are located on the Cu atom and on the axial tyrosine, whereas the equatorial, cysteine-linked tyrosine obtains the unpaired spin upon proton transfer from substrate to axial Tyr.