Abstract
The rate of sugar transport as a function of temperature has been compared in two unsaturated fatty acid auxotrophs. One of these, the parent strain 30E, can β‐oxidize the unsaturated fatty acid supplements, whereas the β‐oxidation defective progeny strain 30Eβox^−^ cannot. In a previous study, Arrhenius plots for transport of β‐glucosides and β‐galactosides by strain 30Eβox^−^ revealed striking departures from linearity at both a lower and an upper characteristic temperatures. By electron spin resonance (esr) these temperatures were shown to correlate with the temperatures where the membrane lipids undergo a transition from a totally solid state to a solid–liquid equilibrium and from a solid–liquid equilibrium to a totally liquid state, respectively (1). In the present study with strain 30E we have made the following observations:
Arrhenius plots for transport rate are usually more complex, often revealing three characteristic temperatures. Two of these correlate with the upper and lower characteristic temperatures observed in strain 30Eβox^−^. The third characteristic temperature falls between the previously described upper and lower ones.
In cells supplemented during growth with elaidate, the third characteristic temperature was identical within experimental limits for both β‐glucoside and β‐galactoside transport. indicating that it is likely to arise from some interaction in the bulk lipid phase. This conclusion is supported by the fact that the boundary of a change in physical state is also observed at this temperature by electron spin resonance.
In cells supplemented during growth with oleate, two or three characteristic temperatures were observed depending upon the transport system studied. Although glucoside and galactoside transport had the same lower characteristic temperature, these systems had no common upper characteristic temperature.
In cells supplemented during growth with the lipid density label, bromostearic acid, three characteristic temperatures were observed for β‐glucoside transport in both strains 30E and 30Eβox^−^.