Effects of Naturally Occurring Polyols and Urea on Mitochondrial F0FjATPase

Adriana dos Passos Lemos, Carlos E. Peres-Sampaio, Horácio Guimarães-Motta, Jerson L. Silva and José R. Meyer-Fernandes* Departamento de Bioqmmica Medica, Instituto de Ciencias Biomedicas, Universidade Federal do Rio de Janeiro (UFRJ), Ilha do Fundäo, 21941-590. Rio de Janeiro, RJ. Brazil. Fax: (+55) (+21) 270-8647. E-mail: [email protected] * Author for correspondence and reprint requests Z. Naturforsch. 55c, 392-398 (2000): received December 8, 1999/February 18, 2000 Polyols, Mitochondrial F0F1-ATPase. Urea We show that urea inhibits the ATPase activity of MgATP submitochondrial particles (MgATP-SMP) with Ki = 0.7 m . probably as a result of direct interaction with the structure of F()F |-ATPase. Counteracting compounds (sorbitol, mannitol or inositol), despite slightly (10-20% ) inhibiting the ATPase activity, also protect the F()Fr ATPase against denaturation by urea. However, this protection was only observed at low urea concentrations (less than 1.5 m ) , and in the presence of three polyols, the Kj for urea shift from 0.7 m to 1.2 m . Urea also increases the initial activation rate of latent MgATP-SMP 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 activation level occurred after 1 h, 30 and 10 min, respectively. At high MgATP-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 urea on the activation of MgATP-SMP depends on time, urea and protein concentrations. It was also observed that polyols suppress the activation of latent 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 F()Fr ATPase may also increase the compactation of protein structure, explaining the inhibi­ tion of natural inhibitor protein of ATPase (IF,) release and the activation of the enzyme.