An alanine carrier protein was isolated from membranes of the thermophilic bacterium PS3 using ion exchange column chromatography followed by high performance liquid chromatography with a hydroxylapatite column. The final preparation consisted of a single polypeptide, with Mr = 42,500, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A polarity index of 33% was calcula...