Kinetic and steady-state investigations of solute accumulation in bacterial membranes by continuously monitoring the radioactivity in the effluent of flow-dialysis experiments.

The flow-dialysis technique for studies of solute accumulation by membrane preparations has been made more suitable for routine measurements by recording continuously the radioactivity in the effluent of a flow-dialysis vessel with a homogeneous flow-monitoring device for beta-emitters. This modification not only decreases the time and cost of a flow-dialysis experiment but also allows the investigator to react directly on the outcome of his experiments. Analysis of the kinetics of this automated flow-dialysis system shows that this technique can also be used for the determination of the rate of uptake of solutes into bacterial membranes. This has been confirmed in Rhodopseudomonas sphaeroides by comparing the results of Rb+ and inorganic phosphate uptake studies performed by automated flow-dialysis and by the conventional filtration procedure. This application has the limitation that solute uptake has to proceed linearly for a period of about five times the half-time of the response of the flow-dialysis system. The two described applications make automated flow-dialysis very well-suited for experiments on the bioenergetics and regulation of solute uptake into bacterial membranes. Both driving force and rate of solute uptake can now be determined in one experiment.