Effects of naturally occurring polyols and urea on mitochondrial F(0)F(1)ATPase

We show that urea inhibits the ATPase activity of MgATP submitochondrial pa rticles (MgATP SMP) with Ki = 0.7 M, probably as a result of direct interac tion with the structure of F0F1-ATPase. Counteracting compounds (sorbitol, mannitol or inositol), despite slightly (10-20%) inhibiting the ATPase acti vity, also protect the F0F1-ATPase against denaturation by urea. However, t his protection was only observed at low urea concentrations (less than 1.5 M), and in the presence of three polyols, the Ki for urea shift from 0.7 M to 1.2 M. Urea also increases the initial activation rate of latent MgATP-S MP in a dose-dependent-manner. However, when the particles (0.5 mg/ml) were preincubated in the presence of 1 M, 2 M or 3 M urea, a decrease in the ac tivation level occurred after 1 h, 30 and 10 min, respectively. At high MgA TP-SMP concentration (3 mg/ml) a decrease in activation was observed after 2 h, 1 h and 20 min, respectively. These data indicate that the effect of u rea on the activation of MgATP-SMP depends on time, urea and protein concen trations. It was also observed that polyols suppress the activation of late nt MgATP-SMP in a dose-dependent manner, and protect the particles against urea denaturation during activation. We suppose that a decrease in membrane mobility promoted by interactions of polyols with phospholipids around the F0F1-ATPase may also increase the compactation of protein structure, expla ining the inhibition of natural inhibitor protein of ATPase (IF1) release a nd the activation of the enzyme.