Ion metabolism in aHalobacterium : II. Ion concentrations in cells at different levels of metabolism.

The changes in concentration of K(+), Na(+) and Cl(-) are given in growing cultures of aHalobacterium species subjected to cold, lack of O2 or starvation. In growing cells, the ion concentration ratios across the cell membrane were 1,000∶1 (inside:outside) for K(+) and 1∶2 for Na(+). In bacteria with a low rate of endogenous metabolism induced by 24-hr starvation, the ratios were 500∶1 for K(+) and 1∶4 for Na(+). O2 and a substrate were required for K(+) uptake in growing bacteria, but not for the maintenance of K(+) and Na(+) gradients in starving bacteria. The exchange of K(+), Na(+) and Li(+) across the cell membrane of starving bacteria was found to have a time constant for 50% completion of the process of 20 to 30 sec. The exchange of cell Cl(-) with NO 3 (-) was a twostage process with time constants of approximately 2 min and 2-1/2 hr. The results are explained in terms of the binding of most of the cell K(+) which brings about the distribution of Na(+) and Cl(-) according to the Gibbs-Donnan equilibrium; the role of metabolism is to induce changes in the mean ion-activity coefficients.