Effects of pressure and pressure antagonists on the growth and membrane-bound ATP-ase of Acholeplasma laidlawii B.

1. Arrhenius plots of the membrane-bound ATP-ase were constructed at pressures of 300, 600 and 900 atm. Pressure shifts the plots to higher temperatures with an increase in slope. 2. These data are partially consistent with a kinetic model in which a phase transition in the lipids associated with the ATP-ase determines the activity of the enzyme. They are also consistent with a model in which the non-linear Arrhenius plot is caused by the low temperature inactivation of the enzyme, upon which pressure acts directly. 3. Pentanol inhibits the ATP-ase without affecting the Arrhenius break temperature, and therefore does not act by affecting the phase-state of lipids associated with the enzyme. The pentanol-enzyme interaction yielded the following: delta H 46 Kcal mol-1 and delta S 114 cal mol-1 deg-1. 4. Pressure inhibits cell growth in a way which is partially offset by comparable partial pressures of helium and hydrogen. Its action probably involves the ordering of the membrane bilayer which is counteracted by the fluidising effect of the gases.