Extrusion of Sodium and Hydrogen Ions as the Primary Process in Potassium Ion Accumulation by Streptococcus faecalis

Abstract

Glycolyzing cells of Streptococcus faecalis accumulate K+ with concurrent extrusion of equivalent amounts of H+ and Na+. An attempt was made to clarify the retionship between the movements of Na+ and K+. Sodium was displaced from cells glycolyzing in the presence of ammonia, diethylamine, tris(hydroxymethyl)aminomethane, and other nitrogenous cations; by contrast, K+ was completely retained. Accumulation of K+ by heterologous exchange for Na+ was not inhibited by antibiotics which facilitate diffusion of K+ across the membrane, but was blocked by proton conductors. The results indicate that extrusion of Na+ and H+ from the cells is a primary, energy-linked process which generates an electrical potential (interior negative); K+ accumulation occurs in response to this potential. Two mutants deficient in K+ accumulation and retention were examined in terms of this model. One mutant is apparently defective in exchange of K+ for H+. In the other mutant, exchange of K+ for Na+ is impaired.

Effects of potassium ions on the electrical and pH gradients across the membrane of Streptococcus lactis cells

“…The Ap measured in the absence of added KCl was about 155 mV by the dye technique and 145 mV by the accumulation of f3-galactoside. The mean is similar to the protonmotive force estimated for E. coli membrane vesicles (16), illuminated Halobacterium halobium cells (13), and respiring Staphylococcus aureus cells (1), but is about 40 to 80 mV lower than the values reported for glycolyzing S. faecalis cells (5,6), respiringE. coli cells (1), and illuminated H. halobium vesicles (17).…”

“…The results reported here can be interpreted as follows: K+ ions are exchanged for H+, in analogy to the systems in S. faecalis cells (4,5,20) and E. coli cells (2). The inward movement of K+ results in a decrease of the Alp.…”

“…A decrease in fluorescence was also observed when arginine rather than glucose was added (data not shown). A relatively greater decrease in fluorescence intensity was observed with cells incubated at extracellular pH 7 than at pH 5 When cells were placed in media of relatively high KCl concentration, the level to which the fluorescence dropped after addition of glucose was higher than without KCl in the medium v ( Fig. 3).…”

Two major potassium uptake systems, KtrI and KtrII, in Enterococcus hirae

“…3). We are aware of the fact that E. hirae does not grow in K -starved medium [11], such that Kdp K -ATPase with a high a¤nity for K (K m = 2 WM) is derepressed in Escherichia coli [14,15]. More than 0.2 mM K in medium was required for cell growth of E. hirae [11].…”

“…Na extrusion from the Na -loaded cells is rate-limiting for the net K uptake [13]. K uptake was not observed by the Na -loaded cells of a mutant de¢cient in Na extrusion [14]. 22 Na -extrusion was examined by JEM2 and JEMK1 cells which were cultured in the same medium as shown in Fig.…”