Biological distribution and physiological role of the beta-ketoadipate transport system

beta-Ketoadipate induces catabolic enzymes in Pseudomonas putida. The compound is transported by a system which also concentrates adipate, a non-metabolizable analogue of beta-ketoadipate. The natural substrate, beta-ketoadipate, competitively inhibits adipate transport with a K1 of 0.04 mM, lower than the Km of 0.23 mM observed with adipate. Transport is inhibited competitively by succinate (K1 1.3 mM) and non-competitively by acetate (K1 5.3 mM). The system has a sharp pH optimum at 5.5. Transport activity is stimulated by a variety of ions, and salt concentrations in excess of 0.1 M are required to achieve optimal rates of influx. The transport system is inhibited by proton conductors and thiol reagents. Membrane vesicle preparations concentrate adipate when supplied with an oxidizable energy source. Induction of the transport system does not allow the rapid utilization of exogenous beta-ketoadipate. Nevertheless, the system has been conserved in the evolution of divergent Pseudomonas species. The selective value of the beta-ketoadipate transport system may lie in its apparent function in chemotaxis and in its ability to control intracellular concentrations of the inducing metabolite, beta-ketoadipate.