FIGURE 6.

Enzymatic activity of DR2231. A and B, screening of purified DR2231 for NTP-PPase activity against (d)NTPs in the presence of 0.623 μm (A) and 0.623 nm enzyme (B). The top row (labeled PPase -) in both panels corresponds to screening of each substrate at 10 μm in the absence of inorganic phosphatase. Hydrolysis of ATP is representative of all NTPs. C, specific activities of DR2231 (0.623 nm) at 5 μm substrate; the inset corresponds to determination of specific activities of substrates at 0.623 μm. D, divalent metal preference of DR2231 for 5 μm dUTP hydrolysis; depicted is the percentage of specific activity of the enzyme in the presence of a divalent metal relative to the specific activity in the presence of Mn²⁺. Enzymatic activity in the absence of divalent metals or in the presence of 20 mm EDTA was not detectable. For details, see “Experimental Procedures,” NTP Pyrophosphatase Assays, Error bars, S.D.