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pubmed:abstractText |
Membrane vesicles from Salmonella typhimurium induced for phosphoglycerate transport, were loaded with pyruvate kinase and ADP by lysing spheroplasts under appropriate conditions. Vesicles so prepared catalyze active transport of proline and serine in the presence of phosphoenolpyruvate; this activity is abolished by the protonophore carbonyl cyanide-m-chlorophenylhydrazone and by the H+-ATPase inhibitor N,N' dicyclohexylcarbodiimide but not by anoxia or cyanide. In contrast, D-lactate-driven active transport is abolished by the hydrazone and by anoxia or cyanide but not by the carbodiimide. Moreover, phosphoenolpyruvate does not drive transport effectively in vesicles that lack the phosphoglycerate transport system. The results are consistent with an overall mechanism in which phosphoenolpyruvate gains access to the interior of the vesicles by means of the phosphoglycerate transporter and is then acted on by pyruvate kinase to phosphorylate ADP. ATP formed inside of the vesicles is then hydrolyzed by the H+-ATPase, leading to the generation of a proton electrochemical gradient that drives H+/solute symport. By using pBR322 as vector and Escherichia coli as host, a fragment of S. typhimurium DNA coding for the phosphoglycerate transport system has been cloned. E. coli membrane vesicles containing the phosphoglycerate transport system also catalyze transport in the presence of phosphoenolpyruvate when they are loaded with pyruvate kinase and ADP.
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