Osmolytes protect mitochondrial F(0)F(1)-ATPase complex against pressure inactivation

We have previously reported that carbohydrates and polyols protect different enzymes against thermal inactivation and deleterious effects promoted by guanidinium chloride and urea. Here, we show that these osmolytes (carbohydrates, polyols and methylamines) protect mitochondrial F(0)F(1)-ATPase against pressure inactivation. Pressure stability of mitochondrial F(0)F(1)-ATPase complex by osmolytes was studied using preparations of membrane-bound submitochondrial particles depleted or containing inhibitor protein (IP). Hydrostatic pressure in the range from 0.5 to 2.0 kbar causes inactivation of submitochondrial particles depleted of IP (AS particles). However, the osmolytes prevent pressure inactivation of the complex in a dose-dependent manner, remaining up to 80% of hydrolytic activity at the highest osmolyte concentration. Submitochondrial particles containing IP (MgATP-SMP) exhibit low ATPase activity and dissociation of IP increases the hydrolytic activity of the enzyme. MgATP-SMP subjected to pressure (2.2 kbar, for 1 h) and then preincubated at 42 degrees C to undergo activation did not have an increase in activity. However, particles pressurized in the presence of 1.5 M of sucrose or 3.0 M of glucose were protected and after preincubation at 42 degrees C, showed an activation very similarly to those kept at 1 bar. In accordance with the preferential hydration theory, we believe that osmolytes reduce to a minimum the surface of the macromolecule to be hydrated and oppose pressure-induced alterations of the native fold that are driven by hydration forces.