The protonmotive force and alpha-aminoisobutyric acid transport in an obligately alkalophilic bacterium.

Abstract

Measurementsof the protonmotive force and studies of solute transport in Bacillus alcalophilus were conducted to ascertain how ceil processes are energized under conditions in which a pH gradient, interior alkaline, cannot be established across the membrane.B. alcalophilus grows on Lmaiate in a range of pH from 9.0 to 11.5, with an optimum at pH 10.5.The electrical potential across the membrane, A+, increases progressively from -84 mV at pH 9.0 to -152 mV at pH 11.5.At pH 10.0 and above a ApH exists, interior acid, increasing from 36 mV at pH 10.0 to 151 mV at pH 11.5.At pH 10.5 and 11, at which growth is excellent, the total transmembrane protonmotive forces were only -80 mV and -15 mV, respectively.Uptake of cu-aminoisobutyric acid (AIB), to concentrations 845-fold greater than the external concentration, occurs only at alkaline pH values, with an optimum at pH 10.5.Saturation kinetics, with a K, for AIB of 9.3 JAM, were observed in the presence of sodium ions.Sodium ions are probably symported with AIB in an electrogenic transport that responds to the A+: (a) addition of sodium chloride and AIB to ceils which are taking up triphenyimethyiphos-phonium+ results in a cessation of TPMP+ uptake; (b) conversely, a variety of agents that abolish A+ inhibit sodium-dependent AIB uptake; and (c) in ceils in which the A$ has been dissipated (which occurs upon incubation in K&O, buffer containing ammonium sulfate), sodium chioride does not stimulate AIB uptake appreciably, but sodium thiocyanate does.The cellular levels of potassium are unusually low, and valinomycin inhibited both AIB and TPMP+ uptake even in the absence ocexternai potassium.Similarly, carbonyl cyanide m-chlorophenylhydrazone caused an expected efflux of protons, but an abolition of A+ occurred concomitantly, rather than an increase in the A+.The A$ might be established, at the highly alkaline pH of these studies, by a K+/H+ antiport such that agents which circumvent this