Electrochemical proton gradient of Brevibacterium linens and its relationship to phenylalanine transport

The proton motive force generated by Brevibacterium linens was determined by the accumulation of radiolabelled tetraphenylphosphonium for transmembrane potential (delta psi) and by the accumulation of benzoate ions for the H+ chemical gradient (delta pH). In resting cells at pH 8.0, the delta psi was 172 +/- 10 mV while delta pH was 9 mV. The additions of valinomycin to B. linens in the presence of 100 mM exogenous potassium reduced the delta psi and led to a drastic inhibition of phenylalanine transport. These findings are consistent with the hypothesis that a membrane potential is essential for active phenylalanine transport in B. linens cells at pH 8.0. Phenylalanine transport in these cells (halotolerant strain) did not depend on the presence of Na+.