The action of 2,4-dinitrophenol on myosin

Abstract

1. 1. The activation of myosin ATPase by 2,4-dinitrophenol at 25 °C. is closely dependent on substrate concentration. Marked stimulation by DNP occurs at ATP concentrations in excess of 1 × 10 −3 M, whereas at concentrations below 1 × 10 −4 M DNP inhibits the enzyme. 2. 2. At 0 °C., DNP inhibits the enzyme over a range of substrate concentrations of 0.8–17 × 10 −4 M. 3. 3. At 25 °C., Zn ++ activates myosin ATPase in concentrations up to 1.5 × 10 −5 M. At 0 °C. and in the presence of DNP at 25 °C., Zn ++ is inhibitory at this concentration. 4. 4. At 25 °C., p-chloromercuribenzoate activates the ATPase at concentrations up to 7 × 10 −7 M. At 0 °C. and in the presence of DNP at 25 °C., PCMB inhibits at this concentration. 5. 5. Proteins enhance DNP activation of myosin ATPase at 25 °C. In the absence of DNP the effect of proteins is negligible at 25 °C. At 0 °C. proteins enhance the ATPase activity. 6. 6. At 25 °C. and at high KCl concentration, activation of myosin ATPase by ethylenediamine tetraacetate in the absence of Ca ++ is much greater than that due to Ca ++ alone. At 0 °C., Ca ++ is the better activator of the two. 7. 7. These results are discussed in relation to published data on the polymerization of myosin at higher temperatures.