FIG. 5.

Phospholipids stimulate NTP hydrolase activities of transport NTPases. (A) TrbB dATP hydrolase activity in the presence of various phospholipids; (B) ATP hydrolase activity of HP0525 in the presence of various phospholipids. NTPase assays were performed in 50 mM Tris-HCl [pH 7.5], 50 mM KCl, 2 mM MgCl₂, 0.05 mg of bovine serum albumin, 1 mM dithiothreitol, and 0.25 mM EDTA. Phospholipids were added to the reactions as sonicated suspensions (see Materials and Methods), and after a preincubation period of 10 min at 30°C, 0.1 μCi of radiolabeled (d)ATP was added (final concentration, 0.2 mM). Incubation was continued for 30 min at 30°C, and the reactions were stopped by the addition of EDTA (final concentration, 50 mM). Products were analyzed by thin-layer chromatography and were quantified as described in Materials and Methods. Symbols: ▴, CL; ●, PG; ■, PE.