Transport of α-aminoisobutyrate by cells and membrane vesicles of Pseudomonas fluorescens

The transport of α-aminoisobutyrate into Pseudomonas fluorescens NCIB 8865 and membrane vesicles prepared from this organism has been studied. Uptake by cells was mediated by two active transport systems with different apparent $\text{K}{}_{\mathrm{<mtext>m</mtext>}}$ values, while transport into membrane vesicles was mediated by a single component. The effect of inhibitors on the energy-coupling mechanism for α-aminoisobutyrate transport in these systems suggests that a membrane potential may play a significant role in supporting α-aminoisobutyrate transport. The magnitude of the membrane potential in the vesicle system, and the sensitivity of its generation to inhibitors, has been measured using ¹³⁷Cs in the presence of valinomycin. Direct attempts to demonstrate a proton-symport mechanism for α-aminoisobutyrate transport were negative.