Mechanism of taurine: α-ketoglutarate dioxygenase (TauD) from Escherichia coli

The iron(II)- and α-ketoglutarate-dependent dioxygenases comprise enzymes that catalyze a variety of important reactions in biology, including steps in the biosynthesis of collagen and antibiotics, the degradation of xenobiotics, the repair of alkylated DNA, and the sensing of oxygen and response to hypoxia. In these reactions, the reductive activation of oxygen is coupled to hydroxylation of the substrate and decarboxylation of the co-substrate, α-ketoglutarate. It is believed that a single, conserved mechanistic pathway for formation of a high-valent iron intermediate that attacks the substrate is operant in all members of this family. Application of a combination of rapid kinetic and spectroscopic techniques to the reaction of taurine/α-ketoglutarate dioxygenase (TauD), one member of this large enzyme family, has led to the detection of two reaction intermediates. The first intermediate, which is termed J, is a high-spin Fe^IV-oxo complex. Decay of J exhibits a large, normal C1 deuterium kinetic isotope effect, demonstrating that it is the species activating the C-H bond for hydroxylation. The second intermediate is an Fe^II-containing product(s) complex.