ISSN:
1432-072X
Keywords:
Methanobacterium thermoautotrophicum
;
Potassium accumulation
;
Membrane potential
;
pH gradient
;
Energy coupling
;
Active transport
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Cultures of Methanobacterium thermoautotrophicum (Marburg) growing on media low in potassium accumulated the cation up to a maximal concentration gradient ([K+]intracellular/[K+]extracellular) of approximately 50,000-fold. Under these conditions, the membrane potential was determined by measuring the equilibrium distribution of the lipophilic cation (14C) tetraphenylphosphonium (TPP+). This cation was accumulated by the cells 350-to 1,000-fold corresponding to a membrane potential (inside negative) of 170–200 mV. The pH gradient, as measured by equilibrium distribution of the weak acid, benzoic acid, was found to be lower than 0.1 pH units (extracellular pH=6.8). The addition of valinomycin (0.5–1 nmol/mg cells) to the culture reduced the maximal concentration gradient of potassium from 50,000-to approximately 500-fold, without changing the membrane potential. After dissipation of the membrane potential by the addition of 12C-TTP+ (2 μmol/mg cells) or tetrachlorosalicylanilide (3 nmol/mg cells), a rapid and complete efflux of potassium was observed. These data indicate that potassium accumulation in the absence of valinomycin is not in equilibrium with the membrane potential. It is concluded that at low extracellular K+ concentrations potassium is not accumulated by M. thermoautotrophicum via an electrogenic uniport mechanism.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00454936
