On the physical state of the intracellularly accumulated substrates of β-galactoside-permease in Escherichia coli

Abstract

The experiments reported in this paper show that osmotically active spheres prepared from E. coli respond osmotically to the addition of galactosides. The characteristic of this response are similar to those of galactoside-permease: inducibility, inhibition by azide, specificity. Furthermore, the increase in internal osmotic pressure manifested by the change in optical density, is of the same order as would be calculated from the total amount of galactoside known to be accumulated by whole cells. It is concluded that the bulk of the intracellular galactoside accumulated by the action of galactoside-permease is a free solute. If any intracellular binding of galactosides occurs, it is quantitatively insignificant. The extension of this conclusion to other permease-like systems is a matter for speculation. The method described is capable of detecting a change in the internal osmotic pressure equivalent to 0.01 M sucrose and probably somewhat less.