Energy Source for Active Transport of α-Aminoisobutyric Acid in KB Cells

Abstract

Abstract The energy source for concentrative transport of α-amino-isobutyric acid (AIB) in KB cells is ATP generated during either anaerobic glycolysis or oxidative phosphorylation. The dependence of AIB accumulation on the concentration of ATP is described by a rectangular hyperbola from which the ATP concentration supporting half-maximal accumulation of AIB was estimated to be 0.8 mm. With the aid of inhibitors and uncouplers of oxidative phosphorylation it was shown that energization of AIB transport by ATP does not involve the participation of high energy intermediates which may be generated within the mitochondria during oxidative phosphorylation or from ATP. Evidence was obtained against the function of phosphoenolpyruvate as the immediate energy donor to the transport system. A kinetic analysis of AIB influx and efflux revealed that ATP and intracellular K+ act on the step involved in AIB uptake by decreasing the Km for AIB influx, whereas oligomycin increases this Km. A comparison of the effectiveness of oligomycin, peliomycin, and ossamycin in inhibiting three distinct biochemical systems, namely, oxidative phosphorylation, AIB transport, and the (Na+ + K+)-ATPase, showed that all three inhibitors are equally effective in inhibiting oxidative phosphorylation, but peliomycin is the most effective in inhibiting the (Na+ + K+)-ATPase. Ossamycin is the least effective in inhibiting the latter and AIB transport.