4-Hydroxybenzoate Uptake in Klebsiella pneumoniae Is Driven by Electrical Potential

The uptake of 4-hydroxybenzoic acid (4-HBA) in intact cells of a mutant of Kiebsiella pneumoniae was investigated. Uptake of 4-HBA was shown to be an inducible system. This uptake system, at pH 7.0, has a high affinity for its substrate (apparent Kt = 13 μM) and a maximal velocity of 27.6 nmol min−1 mg protein−1. Competition studies with various structural analogs indicated a very narrow specificity of the 4-HBA uptake system. The transport system has been inhibited by inhibitors of energy metabolism and its activity has not been detected in the crude shock extracts. The effect of two ionophores, nigericin and valinomycin, on 4-HBA uptake with respect to the external pH has been studied. All observations indicate that 4-HBA uptake is active and energized by the membrane potential.