... [16 18].Interestingly, the sum of ATP and UTP was two-foldhigher than that of CTP and GTP, and the ratio of dATP and dTTP to dCTP and dGTP was also 2 : 1 [16, 17]. This fact is in accordance with the ... after 3 min and thendeclined, while the formation of [3H]ATP was increasedlinearly with time within the first 15 min. After 30 min, the reaction reached equilibrium (Fig. 4A). Furtherexperiments ... substrate in a totalvolume of 20 lL. The reaction was initiated by the addition the enzyme (100 ngÆreaction)1for the determination of NTP synthesis rates and 0.5–1 ngÆreaction)1for the deter-mination...