The effect of temperature and membrane lipid composition on the rate of beta-oxidation by Escherichia coli.

Escherichia coli, strain D-1ML, was grown to mid-exponential phase at 14, 30 or 43 degrees C. Membrane fractions were prepared from cells grown at each temperature and analyzed with respect to the unsaturated to saturated fatty acid ratio and the effect of temperature on the rate of catalysis by succinate dichlorophenol reductase and the membrane-bound acyl-CoA synthetase. The ratio of unsaturated to saturated fatty acids increased from 0.72 : 1.00 in cells grown at 43 degrees C to 1.46 : 1.00 in cells grown at 14 degrees C. The specific activity of succinate dichlorophenol reductase was increased by greater than two-fold in cells grown at 43 degrees C relative to the specific activity of the reductase from cells grown at 14 degrees C. In addition the activity of succinate dichlorophenol reductase responded to thermal phase transitions that were characteristic of membranes isolated from cells grown at the three different temperatures. In contrast the specific activity of acyl-CoA synthetase exhibited little or no variation as a function of the fatty acid composition of the membrane and the activity of the synthetase was not subject to thermal phase transitions. Comparison of Arrhenius plots of the oxidation of [U-14C]palmitoleate by whole cells and acyl-CoA synthetase activity with palmitoleate as substrate demonstrated that the two exhibited virtually identical Arrhenius activation energies and temperature optima. The Arrhenius plots of other soluble beta-oxidation enzymes do not resemble the provile of beta-oxidation. These data strongly suggest that the acyl-CoA synthetase which catalyzes the transport of fatty acids into E. coli by group translocation mechanism is the rate-limiting step in beta-oxidation in E. coli.