Amino acid transport in membrane vesicles of Clostridium thermoautotrophicum

A proton motive force (delta p) generated by oxidation of CO in membrane vesicles of Clostridium thermoautotrophicum drove active transport of L-alanine, glycine and L-serine. The maximum rate (Vmax) for L-alanine transport was 12 X higher at 50 degrees C than at 25 degrees C. The apparent transport constant (Kt) for L-alanine uptake was 30-40 microM and independent of the temperature. Glycine was a substrate for the L-alanine transport system as demonstrated by the competitive inhibition of L-alanine uptake by glycine (Ki = 6 microM), by the kinetics of glycine uptake (Kt = 7 microM) and by the inhibition of glycine uptake by L-alanine. The uptake kinetics of glycine was biphasic. L-Serine inhibited competitively also L-alanine and glycine transport but it was taken up by a separate transport system. The rate of amino acid transport, but not the Kt, was dependent on the value of the proton motive force.