Proton-linked L-rhamnose transport, and its comparison with L-fucose transport in Enterobacteriaceae.
1. An alkaline pH change occurred when L-rhamnose, L-mannose or L-lyxose was added to L-rhamnose-grown energy-depleted suspensions of strains of Escherichia coli. This is diagnostic of sugar-H+ symport activity. 2. L-Rhamnose, L-mannose and L-lyxose were inducers of the sugar-H+ symport and of L-[14C]rhamnose transport activity. L-Rhamnose also induced the biochemically and genetically distinct L-fucose-H+ symport activity in strains competent for L-rhamnose metabolism. 3. Steady-state kinetic measurements showed that L-mannose and L-lyxose were competitive inhibitors (alternative substrates) for the L-rhamnose transport system, and that L-galactose and D-arabinose were competitive inhibitors (alternative substrates) for the L-fucose transport system. Additional measurements with other sugars of related structure defined the different substrate specificities of the two transport systems. 4. The relative rates of H+ symport and of sugar metabolism, and the relative values of their kinetic parameters, suggested that the physiological role of the transport activity was primarily for utilization of L-rhamnose, not for L-mannose or L-lyxose. 5. L-Rhamnose transport into subcellular vesicles of E. coli was dependent on respiration, was optimal at pH 7, and was inhibited by protonophores and ionophores. It was insensitive to N-ethylmaleimide or cytochalasin B. 6. L-Rhamnose, L-mannose and L-lyxose each elicited an alkaline pH change when added to energy-depleted suspensions of L-rhamnose-grown Salmonella typhimurium LT2, Klebsiella pneumoniae, Klebsiella aerogenes, Erwinia carotovora carotovora and Erwinia carotovora atroseptica. The relative rates of subsequent acidification varied, depending on both the organism and the sugar. L-Fucose promoted an alkaline pH change in all the L-rhamnose-induced organisms except the Erwinia species. No L-rhamnose-H+ symport occurred in any organism grown on L-fucose. 7. All these results showed that L-rhamnose transport into the micro-organisms occurred by a system different from that for L-fucose transport. Both systems are energized by the trans-membrane electrochemical gradient of protons. 8. Neither steady-state kinetic measurements nor binding-protein assays revealed the existence of a second L-rhamnose transport system in E. coli.
Muiry
J A
JA
Department of Biochemistry, University of Cambridge, U.K.
Gunn
T C
TC
McDonald
T P
TP
Bradley
S A
SA
Tate
C G
CG
Henderson
P J
PJ
D001667:Binding, Competitive; D001693:Biological Transport, Active; D050260:Carbohydrate Metabolism; D002241:Carbohydrates / Q000494:pharmacology; D003571:Cytochalasin B / Q000494:pharmacology; D004563:Electrochemistry; D004755:Enterobacteriaceae / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism / Q000648:ultrastructure; D005033:Ethylmaleimide / Q000494:pharmacology; D005643:Fucose / Q000378:metabolism* / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008358:Mannose / Q000378:metabolism / Q000494:pharmacology; D010429:Pentoses / Q000378:metabolism / Q000494:pharmacology; D011522:Protons; D012210:Rhamnose / Q000378:metabolism* / Q000494:pharmacology
D002241:Carbohydrates; D010429:Pentoses; D011522:Protons; D005643:Fucose; D003571:Cytochalasin B; C043333:lyxose; D005033:Ethylmaleimide; D008358:Mannose; D012210:Rhamnose