JBC, Vol. 251, Issue 21, 6735-6738, Nov, 1976
Microcalorimetric study of the binding of thiodigalactoside to the lactose permease M protein of Escherichia coli
A. Belaich, P. Simonpietri and J. P. Belaich
The energetics of the binding of thiodigalatoside onto vesicles of
Escherichia coli containing M protein is described. The Kd determined from
equilibrium dialysis was 5-10(-5) M. The enthalpy change (deltaH) was
measured by calorimetry. The derived deltaG and deltaH values allowed
estimation of the entropic change associated with the binding reaction. The
control experiments were made with membranes from cells that were not
induced for the lac system. All the experiments were carried out in
presence of 10(-2) M sodium azide to prevent any concentration of
thiodigalactoside into the vesicles. It was concluded that such membrane
vesicles which are in a de-energized state are able to bine
thiodigalactoside specifically with a Kd corresponding to the Km of the
entry of beta-galactoside measured with intact, active cells.
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