Fig. 4.

dGTPase activity of E. coli Dgt measured using two different techniques. (A) HPLC method. The Dgt (hexamer) concentration was 0.2 nM; the k_cat was calculated at 29.2 ± 1.1 s⁻¹. (B) Enzyme-coupled assay. The protein concentration used was 4 nM; the k_cat was calculated at 17.9 ± 0.6 s⁻¹. The data were fitted to the Hill equation [23]. For the curve of Fig. 4B, an N value > 1 was obtained, indicating a cooperative mechanism for dGTP hydrolysis.