It was of interest to examine whether rNSs could cleave dATP. As shown in Fig. 4B , rNSs could also use dATP as substrate and the kinetic parameters obtained from the Lineweaver-Burk plot (Fig. 4B inset) are also presented in table 2. The k cat for dATP was approximately 10 times lower than that of ATP, although the K M (15.5 mM) was much lower. The specificity of rNSs was also tested by using the ATP analog, adenosine 59 (b, c imido) triphosphate. 5 mM concentration of this ATP analog resulted in considerable decrease in the activity (Fig. 4C lane 4 and 5) . Further increase in the concentration of the analog abolished the product formation completely (Fig. 4C lane 6 to lane 9) .