L-carnitine uptake by Escherichia coli.

The uptake of L-carnitine by Escherichia coli 044 K74 which is able to metabolize L-carnitine to gamma-butyrobetaine under anaerobic conditions was studied. The uptake system of E. coli was induced in the presence of L-carnitine or crotonobetaine. The optimum influx of L-carnitine was found to take place at 37 degrees C in phosphate buffer, pH 7.5. On the basis of the temperature dependence of the uptake rate an activation energy of 53.5 kJ/mol was estimated. The transport of L-carnitine was energy dependent. The kinetics of L-carnitine entry followed the Michaelis-Menten relationship yielding a Km value of 5.3 x 10(-4) M and a Vmax of 154 nmol/min.mg protein. The transport system showed considerable structural specificity for trimethylamine carboxylic molecules. The results suggest that E. coli possesses an inducible, active and carrier-mediated uptake system for L-carnitine.