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Differences in uncoupling effects associated with the uptake of lactose and dansyl galactoside in escherichia coli membrane active transport vs. specific binding


, : Differences in uncoupling effects associated with the uptake of lactose and dansyl galactoside in escherichia coli membrane active transport vs. specific binding. Archives of Biochemistry and Biophysics 202(1): 126-136

Cytoplasmic membrane vesicles isolated from E. coli take up dansyl-galactoside, a fluorescent competitive inhibitor of lactose transport, to much lower levels than lactose. An initial interpretation, based on the study of the fluorescent changes accompanying the energy-dependent uptake, was that it represented a one-to-one specific binding to the lac carrier protein which was not followed by transport. Recently, on the basis of a new estimation of the number of lac carrier in the membrane, it was advanced that the uptake of dansyl-galactoside represents a nonspecific binding on the inner surface of the membrane following transport. One discriminates between the 2 interpretations by comparing the effects of lactose and dansyl-galactoside uptake on the electrochemical gradient of protons (.DELTA.hivin.mu.H+), generated by the oxidation of substrates, and on the uptake of proline. Indeed, it is known that the rate of lactose transport is such that it leads, as a consequence of the lactose/H+ symport, to an observable decrease of .DELTA.hivin.mu.H+, and secondary to this decrease to an inhibition of the uptake of proline transported at much lower rate. The rates of uptake of lactose and dansyl-galactoside by the membrane vesicles are similar; yet the uptake of dansyl-galactoside does not lead to the uncoupling effects which are associated with the uptake of lactose. The possible reasons for the absence of this uncoupling effect are discussed and the data are incompatible with the notion that the energy-dependent uptake of dansyl-galactoside is associated with an active transport involving a dansyl-galactoside/H+ symport. The data substantiate the initial interpretation that the energy-dependent uptake of dansyl-galactoside reflects the binding to the lac carrier not followed by transport.

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Related references

Ghazi, A.; Therisod, H.; Shechter, E., 1980: Differences in uncoupling effects associated with the uptake of lactose and dansyl-galactoside in Escherichia coli membrane: active transport versus specific binding. Archives of Biochemistry and Biophysics 202(1): 126-136

Lancaster, J.R.Jr ; Hinkle, P.C., 1977: Studies of the beta galactoside transporter in inverted membrane vesicles of escherichia coli part 2 symmetrical binding of a dansyl galactoside induced by an electrochemical proton gradient and by lactose efflux. The binding of 6'-(N-dansyl)aminohexyl-D-thiogalactoside (DG6) to inverted vesicles of E. coli was measured by fluorescence enhancement. As previously observed with right side-out vesicles, binding of DG6 to the vesicles was dependent on effl...

Therisod, H.; Letellier, L.; Weil, R.; Shechter, E., 1977: Functional lac carrier proteins in cytoplasmic membrane vesicles isolated from Escherichia coli. 1. Temperature dependence of dansyl galactoside binding and beta-galactoside transport. Biochemistry 16(17): 3772-3776

Therisod, H.; Letellier, L.; Weil, R.; Shechter, E., 1977: Functional lac carrier proteins in cytoplasmic membrane vesicles isolated from escherichia coli part 1 temperature dependence of dansyl galactoside binding and beta galactoside transport. Dansyl galactoside (6'-N-dansyl)aminohexyl 1-thio-.beta.-D-galactopyranoside) binds in an energy-dependent way to the lac carrier proteins of membrane vesicles isolated from E. coli cells. The binding is not followed by transport but is accom...

Therisod, H.; Weil, R.; Shechter, E., 1978: Functional lac carrier protein in cytoplasmic membrane vesicles isolated from Escherichia coli: temperature and pH dependence of dansyl-galactoside binding. 6'-(N-Dansyl)aminohexyl-1-thio-beta-D-galactopyranoside binds specifically to the lac carrier protein in cytoplasmic membrane vesicles isolated from Escherichia coli. Binding can be induced by substrate oxidation (generation of an electrochem...

Wright, J.K.; Overath, P., 1984: Purification of the lactose:H+ carrier of Escherichia coli and characterization of galactoside binding and transport. The lactose carrier, a galactoside:H+ symporter in Escherichia coli, has been purified from cytoplasmic membranes by pre-extraction of the membranes with 5-sulfosalicylate, solubilization in dodecyl-O-beta-D-maltoside, Ecteola-column chromatograph...

Brabetz, W.; Liebl, W.; Schleifer, K.H.inz, 1993: Lactose permease of Escherichia coli catalyzes active b-galactoside transport in a gram-positive bacterium. Evidence was found for the functional expression of Escherichia coli lactose permease (LacY) in the gram-positive Corynebacterium glutamicum. LacY was shown to be integrated into the cytoplasmic membrane of C. glutamicum. It was also found that th...

Wright J.K.; Overath P., 1984: Purification of the lactose hydrogen ion carrier of escherichia coli and characterization of galactoside binding and transport. The lactose carrier, a galactoside-galactose-H+:H+ symporter in E. coli, was purified from cytoplasmic membranes by pre-extraction of the membranes with 5-sulfosalicylate, solubilization in dodecyl-O-.beta.-D-maltoside, Ecteola-column chromatograp...

Brabetz, W.; Liebl, W.; Schleifer, K.H., 1993: Lactose permease of Escherichia coli catalyzes active beta-galactoside transport in a gram-positive bacterium. The following several lines of evidence demonstrate that lactose permease (LacY) of Escherichia coli is assembled into the cytoplasmic membrane of gram-positive Corynebacterium glutamicum, expressing the lacY gene, as a functional carrier protein....

Kaback, H.R.; Barnes, E.M., 1971: Mechanisms of active transport in isolated membrane vesicles. II. The mechanism of energy coupling between D-lactic dehydrogenase and beta-galactoside transport in membrane preparations from Escherichia coli. Journal of Biological Chemistry 246(17): 5523-5531