Amino acid transport in membrane vesicles ofClostridium thermoautotrophicum

A proton motive force (Δp) 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 × higher at 50°C than at 25°C. The apparent transport constant (Kt) for l-alanine uptake was 30–40 μM 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 μM), by the kinetics of glycine uptake (Kt= 7 μM) and by the inhibiton 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.