Effects of mercury (II) compounds on the activity of dUTPases from various sources

The deoxyuridine triphosphate nucleotidohydrolases (dUTPases, EC 3.6.1.23) from Escherichia coli K-12-, Acholeplasma laidlawii B-PG9-, human KB cell-, and the herpes simplex virus (HSV) type 1- and 2-induced dUTPases were purified and used to determine the effect of various mercury (II) compounds on their activities. Mercuric acetate, 5-mercuri-dUTP (HgdUTP), and 5-mercuri-dCTP (HgdCTP) acted as irreversible active site-directed inhibitors of the dUTPases purified from eukaryotic organisms but not those from prokaryotic organisms. The inhibition constants (K(i)) were estimated for the KB, HSV-1, and HSV-2 dUTPases to be 8 ± 2, 12 ± 3, and 9 ± 2 μm for mercuric acetate, 204 ± 25, 121 ± 15, and 111 ± 10 μm for HgdUTP, and 775 ± 25 and 651 ± 23 μm for HgdCTP, respectively. The conversion of HgdUTP to its mercurithio-derivative resulted in a decrease in the affinity of the derivative for the eukaryotic dUTPases. The 5-mercurithioethylene glycol derivative of dUTP did not act as a substrate for the KB dUTPase but it did act as a substrate for the HSV-1 and HSV-2-induced dUTPases with K(i) values of 526 ± 47 and 483 ± 32 μm, respectively. These results demonstrate that the eukaryotic dUTPases can be distinguished based upon differences in their affinities for the mercurithio-derivatives of dUTP and suggest that there are differences in the steric binding properties of the nucleotide-binding site of these enzymes.