FIGURE 6.

Nucleotidase activity of Drosophila CG3362 measured by a colorimetric assay for inorganic phosphate. A, time course of phosphate release with m⁷GMP and GMP is shown. Enzyme was used at a concentration of 13.8 nm and substrates at 200 μm. The standard deviation, based on three independent experiments, is shown. B, titration of m⁷GMP and GMP is shown. Enzyme concentrations of 13.8–55 nm were used to determine initial rates. Curves were fitted to the Michaelis-Menten equation. C, titration of AMP is shown. Enzyme was used at a concentration of 1.4 μm. The data were fitted as described under “Experimental Procedures.” D, time courses of phosphate release from m⁷GDP are shown. Enzyme was used at 2.8 μm and substrate at 200 μm. The reactions were carried out with or without the addition of 1 unit of pyrophosphatase per 100 μl reaction, as indicated.