The specificity of cleavage of nucleotide triphosphate by rNSs was examined using [c-32 P] labelled ATP and GTP or [a-32 P] CTP, UTP and dATP as substrates. The activity was monitored by TLC as described earlier. The amount of product (NDP or Pi) released was quantitated and the substrate saturation curves as well as Lineweaver-Burk plots were drawn for each of the substrates as described in material and methods section. Fig. 4A depicts the substrate saturation curve with ATP as the substrate. Inset to Fig. 4A shows the Lineweaver-Burk plot of the same data. The K M and k cat values were calculated to be 515.2 mM and 10.8610 23 sec 21 respectively. Similar experiments were performed with the other NTPs. rNSs was able to hydrolyze all the NTPs and the K M and k cat values obtained are presented in table 2. Although the k cat value was the highest with ATP, the K M was also increased by an order of magnitude compared to other NTPs.