Figure 2. The catalytic iron centre of a typical 2-oxoglutarate (2-OG)-dependent dioxygenase.

Of six co-ordinate positions, three are used to bind the 2-histidine-1-carboxylate ‘facial triad’ of the apo-enzyme, two are used to bind the cosubstrate 2-oxoglutarate and the sixth is occupied by a water molecule or (upon activation of the enzyme) molecular oxygen. Potentially, these interactions provide signalling interfaces with molecular oxygen, redox stresses and metabolism.