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 (Ki) were estimated for the KB, HSV-1, and HSV-2 dUTPases to be 8 +/- 2, 12 +/- 3, and 9 +/- 2 microM for mercuric acetate, 204 +/- 25, 121 +/- 15, and 111 +/- 10 microM for HgdUTP, and 775 +/- 25 and 651 +/- 23 microM 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 Ki values of 526 +/- 47 and 483 +/- 32 microM, 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.