Does pressure antagonize anesthesia? High-pressure stopped-flow study of firefly luciferase and anatomy of initial flash.

The antagonizing effect of high pressure against anesthesia is well known. With purified firefly luciferase, however,. Biophys. J. 60:1309-1314) reported that high pressure did not affect the initial flash intensity. Firefly luciferase emits a burst of light when the substrates luciferin and ATP are added in the presence of O2. The light intensity decays rapidly and the weak light lasts for hours. The initial flash is a transient event and is not in a steady state. The steady state is represented by the slope of the linear part of the integral of the light output. The present study used a high-pressure stopped-flow system to compare the pressure effects on the initial flash intensity and the steady-state light intensity. The flash intensity did not change by the application of hydrostatic pressure in the presence or absence of chloroform or 1-octanol. In contrast, high pressure increased the steady-state light intensity. The application of 12 MPa pressure increased the steady-state light intensity of firefly luciferase inhibited by 5 mM chloroform or 0.7 mM 1-octanol by 19.7% and 18.8%, respectively. When analyzed by the rapid reaction kinetics of the transition state theory, the initial peak intensity represents the total amount of active enzyme and is unrelated to the reaction rate. Anesthetics inhibited the initial flash by unfolding the protein, thereby decreasing the concentration of the active enzyme. Pressure affected the steady-state light intensity by changing the reaction rates.