Identification and partial characterization of rabbit brain deoxyuridine 5'-triphosphatase

Adult rabbit brain contains the enzymatic machinery to convert deoxyuridine to deoxyuridine triphosphate (dUTP). Although dUTP as dUMP can be readily incorporated into DNA in place of thymidine monophosphate, we detected no (3H)dUMP in newly synthesized (3H)DNA in adult rabbit brain after the intraventricular injection of (3H)deoxyuridine. Only (3H)thymidine was detected. The probable explanation for the lack of incorporation of uracil into adult rabbit brain DNA is the presence of a specific, high affinity dUTPase which converts dUTP to dUMP and PP. After homogenization and ammonium sulfate fractionation of adult rabbit brain (35 to 75% saturation), a high affinity, specific dUTPase was detected in the dialyzed enzyme preparation. The Km and Vmax of the dUTPase were 0.2 microM and 36 pmol/mg protein/min, respectively. No high affinity dUTPase activity was detectable in liver. In brain, another enzyme hydrolyzed dUTP and dTTP (NTPase( to their respective diphosphates. NTPase, unlike dUTPase, was not sensitive to heating at 65 degrees C for five minutes. Thus, brain, like other tissues, contains a high affinity, specific dUTPase presumably to "sanitize" the cells of dUTP and, thus, protect the integrity of newly synthesized DNA.