Reconstituted Cl− pump protein: A novel ion(Cl−)-motive ATPase
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Cl− absorption by theAplysia californica foregut is effected through an active Cl− transport mechanism located in the basolateral membrane of the epithelial absorptive cells. These basolateral membranes contain both Cl−-stimulated ATPase and ATP-dependent Cl− transport activities which can be incorporated into liposomes via reconstitution. Utilizing the proteoliposomal preparation, it was demonstrated that ATP, and its subsequent hydrolysis, Mg2+, Cl−, and a pH optimum of 7.8 were required to generate maximal intraliposomal Cl− accumulation, electrical negativity, and ATPase activity. Additionally, an inwardly-directed valinomycininduced K+ diffusion potential, making the liposome interior electrically positive, enhanced both ATP-driven Cl− accumulation and electrical potential while an outwardly-directed valinomycininduced K+ diffusion potential, making the liposome interior electrically negative, decreased both ATP-driven Cl− accumulation and electrical potential compared with proteoliposomes lacking the ionophore. Either orthovanadate orp-chloromercurobenzene sulfonate inhibited both the ATP-dependent intraliposomal Cl− accumulation, intraliposomal negative potential difference, and also Cl−-stimulated ATPase activity. Both aspects of Cl− pump transport kinetics and its associated catalytic component kinetics were the first obtained utilizing a reconstituted transporter protein. These results strongly support the hypothesis that Cl−-ATPase actively transports Cl− by an electrogenic process.
Key wordsIon-motive ATPase chloride pump catalytic and transport kinetics electrogenic
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- Gerencser, G. A., and Lee, S. H. (1985b).Biochim. Biophys. Acta 816, 415–417.Google Scholar
- Gerencser, G. A., and Zelezna, B. (1992).Zool. Sci. 9, 925–939.Google Scholar
- Pedersen, P. L., and Carafoli, E. (1987).Trends Biochem. Sci. 12, 146–150.Google Scholar
- Rothstein, A. (1970).Current Topics in Membranes and Transport (Bronner, F., and Kleinzeller, A., eds.), Academic Press, New York, pp. 135–176.Google Scholar
- Slayman, C. L., and Zuckier, G. R. (1989). InBicarbonate, Chloride, and Proton Transport Systems (Durham, J., and Hardy, M., eds.),Ann. N.Y. Acad. Sci. 574, 233–245.Google Scholar