Carbohydrates protect mitochondrial F0F1-ATPase complex against thermal inactivation

Organisms and cellular systems are required to adapt to stress conditions l ike high temperature, often responding by accumulating organic solutes, suc h as sugars. This accumulation is associated with the effectiveness of thes e osmolytes in minimizing protein denaturation and membrane damage under st ress conditions. In this work, we have studied the effect of sugars on the protection against thermal inactivation of mitochondrial F0F1-ATPase comple x, in preparations of submitochondrial particles containing or depleted of inhibitor protein. We observed that after 15 min of pre-incubation at 70 de grees C of latent MgATP-submitochondrial particles (with inhibitor protein) in the presence of 1.5 M of sucrose or trehalose, or 3.0 M of glucose or f ructose, about 80% of enzyme activity remained active. In the same conditio ns, but in the absence of sugars, the activity of the particles was complet ely abolished, Submitochondrial particles depleted of the inhibitor protein (AS-particles) were almost completely inactivated after 3 min of pre-incub ation at 70 degrees C in the absence of sugars and more than 60% of the enz yme activity remained active when these particles were pre-incubated in the presence of sugars. In such condition, the enzyme acquires a more compact and heat-stable conformation. Sugars, as well as the inhibitor protein. inh ibit reversibly F0F1-ATPase complex activity and protect this enzyme agains t inactivation by high temperature. Interestingly, the protection, promoted by sugars, of particles containing inhibitor protein is higher than of par ticles depleted of inhibitor protein, suggesting a synergism between sugar and inhibitor protein.