The state of energization of the membrane of Escherichia coli as affected by physiological conditions and colicin K

Abstract

The bacterial protein colicin K, when added to sensitive E. coli in the presence of 3,3''-dihexyloxacarbocyanine, causes a doubling in fluorescence of the probe. Glucose and O2 cause a decreased fluorescence while anoxia and cyanide cause a rise in fluorescence. Colicin K apparently causes a depolarization of the transmembrane electrical potential. Fluorescence in the absence of colicin K was relatively independent of KCl, NaCl and MgCl2 concentrations below 0.1 M. Although colicin K caused rapid efflux of the K+ analogue 86Rb+, the fluorescence rise was only partially blocked by 0.13 M KCl. The level of fluorescence caused by the action of colicin K was inversely proportional to the logarithm of the concentration of MgCl2 over the range of 2 .mu.M-4 mM. A Nernst electrochemical potential for an anion may counteract a membrane depolarization caused by colicin. After colicin K action, the fluorescence of the carbocyanine could be further increased by anoxia or cyanide. The distribution of the weak base dimethyloxazolidinedione indicated that the pH in the interior of aeroboic E. coli supplied with lactate was alkaline by 0.1 unit and unaffected by colicin. Colicin K apparently does not completely depolarize the membrane potential and does not interfere with the component of membrane energization generated by electron transport. Colicin K does not act as a cationophore. The partial depolarization of the membrane may account for the inhibition of active solute transport caused by colicin K.