Mechanism of dTTP Inhibition of the Bifunctional dCTP Deaminase:dUTPase Encoded by Mycobacterium tuberculosis

Recombinant deoxycytidine triphosphate (dCTP) deaminase from Mycobacterium tuberculosis was produced in Escherichia coli and purified. The enzyme proved to be a bifunctional dCTP deaminase:deoxyuridine triphosphatase. As such, the M. tuberculosis enzyme is the second bifunctional enzyme to be characterised and provides evidence for bifunctionality of dCTP deaminase occurring outside the Archaea kingdom. A steady-state kinetic analysis revealed that the affinity for dCTP and deoxyuridine triphosphate as substrates for the synthesis of deoxyuridine monophosphate were very similar, a result that contrasts that obtained previously for the archaean Methanocaldococcus jannaschii enzyme, which showed approximately 10-fold lower affinity for deoxyuridine triphosphate than for dCTP.