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E M Barnes

Publications and source records attributed to E M Barnes.

108 records · Page 6Linked to original sources
PubMed1970

Beta-galactoside transport in bacterial membrane preparations: energy coupling via membrane-bounded D-lactic dehydrogenase.

The transport of beta-galactosides by isolated membrane preparations from Escherichia coli strains containing a functional y gene is markedly stimulated by the conversion of D-lactate to pyruvate. The addition of D-lactate to these membrane preparations produces a 19-fold increase in the initial rate of uptake and a 10-fold stimulation of the steady-state level of intramembranal lactose or thiomethylgalactoside. Succinate, DL-alpha-hydroxybutyrate, and L-lactate partially replace D-lactate, but are much less effective; ATP and P-enolpyruvate, in addition to a number of other metabolites and cofactors, do not stimulate lactose transport by the vesicles. Lactose uptake by the membrane preparations in the presence of D-lactate requires oxygen, and is blocked by electron transport inhibitors and proton conductors; however, uptake is not significantly inhibited by high concentrations of arsenate or oligomycin. Furthermore, the P-enolpyruvate-P-transferase system is not involved in beta-galactoside transport by the E. coli membrane vesicles. The findings indicate that the beta-galactoside uptake system is coupled to the membrane-bound D-lactic dehydrogenase via an electron transport chain but does not involve oxidative phosphorylation.

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PubMed1969

Control of fatty acid composition in phospholipids of Escherichia coli: response to fatty acid supplements in a fatty acid auxotroph.

The effect of exogenous unsaturated fatty acids on the fatty acid composition of phospholipids of a mutant of E. coli has been examined. These exogenous acids serve as growth factors for an auxotroph requiring unsaturated fatty acids. When each member of a structurally homologous series of cis-unsaturated fatty acids serves as a growth factor, the percentage of unsaturated fatty acid present in phospholipids increases with increasing chain length or decreasing number of double bonds in the apolar chain of the supplement. At 37 degrees , trans-octadecenoic acids support growth and are incorporated into phospholipids at levels higher than the corresponding cis-acids. However, a temperature shift to 27 degrees with trans-acids results in loss of viability and lysis. Utilization of cis-acids as supplements at decreasing temperatures between 42 degrees and 27 degrees results in increasing amounts of unsaturated fatty acids in phospholipids with decreasing temperature. These observations suggest the operation of a regulatory mechanism which controls the composition of saturated versus unsaturated acids in order to maintain the physical properties of phospholipids within narrow limits.

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