BIOLOGICAL TRANSPORT 



i r 



Oh 

 O 



c 



O 



100 h — " T & P 



4-1 



- -H 



C 



3 90 h 



Noninduced + thiomethylgalactoside 



.S 80 



70 



Induced, no galactoside 



\ 



Induced + thiomethylgalactoside 



Induced -f- lactose 



10 



20 



30 



40 



50 



60 



mm 



Figure 12 The effect of adding /3-galactosides (0.01 M) on the 

 optical density of osmotically sensitive E. coli spheroplasts. The optical 

 density changes measure the degree of swelling. [From Sistrom, W. R. 

 (1958), Biochim. et Biophys. Acta, 29, 584; with permission.} 



trative activity of the cell could be recorded in an extracellular 

 fluid. 



For solutes with a net charge, such as potassium or sodium ions, 

 particular care must be taken to verify that net migration actually 

 occurs against the electro chemical gradient, i.e., that a potential 

 gradient across the membrane does not account for the develop- 

 ment of a chemical gradient. Biological phases usually contain non- 

 diffusible, macromolecular anions, which characteristically produce 

 Gibbs-Donnan effects, including potential differences and gradients 



3 2 



