The entry process as the target for energy input in active transport of alpha-aminoisobutyric acid by Mycobacterium...

Mycobacterium phlei was shown to accumulate alpha-aminoisobutyric acid, establishing a concentration gradient of approximately 15,000-fold. The apparent affinity constant of the carrier for alpha-aminoisobutyric acid was 1.8 microM. The system exhibited a broad specificity provided two structural requirements were satisfied: the presence of a free amino and carboxyl group on the alpha carbon and the absence of a net charge. The role of energy coupling on the accumulation of alpha-aminoisobutyric acid was studied by two different kinds of experiments, the relative effects of the inhibitors on the rate of entry and the steady-state of accumulation, and a comparison of the efflux induced at the final steady state by the addition of (a) excess nonradioactive alpha-aminoisobutyric acid, (b) energy inhibitors, or (c) both. The results are consistent with the hypothesis that accumulation of alpha-aminoisobutyric acid is due to an increased rate of entry, the rate of exit not being affected by metabolic inhibitors.