Further properties of sodium ion-stimulated alpha-[1-14C]aminoisobutyric acid uptake in alkalophilic Bacillus species.

Alkalophilic Bacillus No. 8-1 and No. 10A-2, isolated on alkaline media containing NaHCO3 and K2CO3, respectively, required Na+ specifically for the uptake of alpha-aminoisobutyric acid (AIB) into the cells. The K+ added to the uptake medium inhibited the accumulation of AIB in the cells of Bacillus No, 8-1, acting as a competitive inhibitor of the system. Sodium ion prevented the release of AIB from pre-loaded cells. Both potassium and lithium ions had the effect of retaining the AIB pool. The Vmax value for transport increased about five-fold when the pH value of medium was raised from 7 to 9, whereas the Km value decreased with the increase of concentration of sodium ion in the medium of pH 7 or 9. Sodium ion gradient across the membrane caused transient uptake by AIB by membrane vesicles of Bacillus No. 8-1.