The design and use of a hydraulically operated upward pressure-jump

The construction of a hydraulically operated upward pressure-jump is described. Previous instruments with a comparable rate of pressurization used helium gas to pressurize an observation cell to approximately half of the operating pressure reached with the present design. The above instrument, which can pressurize the observation cell in 1.8-3.8 ms, is safe to use and has a maximum working pressure of 30 MPa (300 atm). The device is compact in design and can easily be fitted to any observation cell capable of withstanding the transient change in pressure and of effectively damping cell resonances. The instrument finds specific application in the study of macromolecular equilibria with a large difference in volume between the equilibrium partners. This allows the system to be perturbed far from the equilibrium position at atmospheric pressure; the relaxations obtained can be analysed as essentially unidirectional processes. Kinetic data for the reverse reaction would be obtained from experiments in a conventional downward pressure-jump. A study on the kinetics of the self-assembly of the myosin thick-filament is presented as a practical example.