L-Malate transport and proton symport in vesicles prepared from Pseudomonas putida

Abstract

In vesicles from glucose-grown Pseudomonas putida, L-malate is transported by nonspecific physical diffusion. L-Malate also acts as an electron donor and generates a proton motive force (Δp) of 129 mV which is composed of a membrane potential (Δψ) of 60 mV and a ΔpH of 69 mV. In contrast, vesicles from succinate-grown cells (a) transport L-malate by a carrier-mediated system with a Km value of 14.3 mM and a Vmax of 313 nmol∙mg protein−1∙min−1, (b) generate no Δψ, ΔpH, or Δp when L-malate is the electron donor, and (c) produce an extravesicular alkaline pH during the transport of L-malate. A kinetic analysis of this L-malate-induced proton transport gives a Km value of 16 mM and a Vmax of 667 nmol H+∙mg protein−1∙min−1. This corresponds to a H+/L-malate ratio of 2.1. The failure to generate a Δp in these vesicles is considered, therefore, to be consistent with the induction in succinate-grown cells of an electrogenic proton symport L-malate transport system.