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P-type ATPases are membrane proteins acting as ion pumps that drive an active transport of cations across the membrane against a concentration gradient. The required energy for the ion transport is provided by binding and hydrolysis of ATP. A reaction mechanism of ion transport and energy transduction is assumed to be common for all P-type ATPases and generally described by the Post-Albers cycle. Transient currents and charge translocation of P-type ATPases were extensively investigated by electrical measurements that apply voltage jumps to initiate the reaction cycle. In this study, we simulate an applied voltage across the membrane by an electric field and perform electrostatic calculations in order to verify the experimentally-driven hypothesis that the energy transduction mechanism is regulated by specific structural elements. Side chain conformational and ionization changes induced by the electric field are evaluated for each transmembrane helix and the selectivity in response is qualitatively analyzed for the Ca2+-ATPase as well as for structural models of the Na+/K+-ATPase. Helix M5 responds with more conformer changes as compared to the other transmembrane helices what is even more emphasized when the stalk region is included. Thus our simulations support experimental results and indicate a crucial role for the highly conserved transmembrane helix M5 in the energy transduction mechanism of P-type ATPases.
TABLE OF CONTENTS (here without authors) Introduction 1. Em Busca dos Sítios do Poder na África Centro Ocidental. Homens e Caminhos, Exércitos e Estradas (1483-1915) 2. The Supply and Deployment of Horses in Angolan Warfare (17th and 18th Centuries) 3. Wagon Technology, Transport and Long-distance Communication in Angola 1885-1908 4. Trade, Slavery, and Migration in the Interior of Benguela: The Case of Caconda, 1830-1870 5. The Economics of the Kwango Rubber Trade, c. 1900 6. As Vias de Comunicação e Meios de Transporte como Factores de Globalização, de Estabilidade Política e de Transformação Económica e Social: Caso do Caminho-de-ferro de Bengela (Benguela) (1889-1950) 7. Nas Malhas da Rede: Aspectos do impacto económicoe social do transporte rodoviário na região do Huambo c. 1920-c. 1960 8. Communications between Angola and East Central Africa Before c. 1700 9. Long-distance Caravans and Communication beyond the Kwango (c. 1850-1890) 10. A Escrita em Angola: Comunicação e Ruído entre as Diferentes Sociedades em Presença 11. Escrever o Poder: Os Autos de Vassalagem e a Vulgarização da Escrita entre as Elites Africanas Ndembu 12. Do Passado ao Presente: Tráfego Comercial e Redes de Comunicação, Factores Privilegiados de “Modernidade” 13. Refugees on Routes. Congo / Zaire and the War in Northern Angola (1961-1974) 14. Crossing the River: Myth and Movement in Central Africa 15. From Group Mobility to Individual Movement: The Colonial Effort to Turn Back History Notes on Contributors