Activation of the β-galactoside transport system in escherichia coli ML-308 by n-alkanols. Modification of lipid-protein interaction by a change in bilayer fluidity

Abstract

The net rate of transport of o- nitrophenyl-β- d- galactopyranoside by Escherichia coli ML-308 is increased at temperatures below the apparent phase transition of the lipid bilayer in the presence of n-alkanols. The degree of activation produced is determined both by the concentration and chain length of the n-alkanol used. At low concentrations n-alkanols “activate” transport, but do not cause either cell lysis or denaturation of β-galactosidase. Arrhenius plots of the kinetic constants for transport indicate the K m shows discontinuity with increasing temperature, while the slope for V changes only gradually. The presence of 10.5 mM n-hexanol increases the value of both K m and V at low temperature. A comparison of these data to those obtained at a single substrate concentration (1.85 mM o-nitrophenyl-β- d-galactopyranoside) suggests the biphasic behavior of Arrhenius plots at that concentration may be attributed to changes in the K m for the transport process.