FIGURE 4.
The MgATPase activity of myosin-18A isoforms is low and is poorly activated by actin. Time course of ATP hydrolysis measured used an NADH-coupled assay where the decline in absorbance at 340 nm reflects the course of ATP hydrolysis. Open triangle, 30 μm F-actin alone; open diamond, myosin-18Aα-S1 alone; closed diamond, 30 μm actin plus myosin-18Aα-S1; open square, myosin-18Aβ-S1 alone; closed square, myosin-18Aβ-S1 plus 30 μm F-actin. The data were arithmetically normalized to a starting absorbance value of 1.0. Experiments shown were conducted at 25 °C in a buffer containing 50 mm KCl, 10 mm MOPS (pH 7.2), 2 mm MgCl2, 0.15 mm EGTA, 2 mm ATP, 40 units/ml lactate dehydrogenase, 200 units/ml pyruvate kinase, 1 mm phosphoenolpyruvate, and 200 μm NADH. The concentration of myosin-18A motors used in these traces was 1 μm. AU, absorbance units.