Studies on the Mechanism of Potassium-stimulated Respiration in Escherichia coli

Abstract

Summary: The inter-relationship between the intracellular concentration of potassium ions and the rate of oxidation of glutamate was investigated in washed Escherichia coli. The time-curve of glutamate oxidation by the potassium-depleted coli showed a marked lag phase and the rate of oxygen uptake increased concurrently with the accumulation of potassium ions. After a constant intracellular potassium concentration was reached, the rate of oxidation remained constant. Carbonyl cyanide m-chlorophenylhydrazone (m-C1-CCP) and methylene blue inhibited the respiration when added to the reaction mixture during the initial phase of K+ accumulation. The extent of inhibition induced by these compounds was inversely related to the rate of oxidation prevailing at the time of their addition. No inhibition resulted when the substances were added after the K+ accumulation and respiratory rate had reached the steady state values. Pre-incubation with glucose and KC1 abolished the initial lag of glutamate oxidation as well as the inhibitory action of m-C1-CCP. It is concluded that the intracellular concentration rather than the flux of potassium ion governs the control of respiration in E. coli. The possible relation of the mode of respiratory inhibition induced by m-C1-CCP and methylene blue to the known ability of these compounds to uncouple oxidative phosphorylation, is discussed in terms of the presumed energy requirements of the system mediating the K+ transport.