Function, Structure, and Evolution of the Major Facilitator Superfamily: The LacY Manifesto
Figure 3
Artificial translocation modes. (a) Schematics of equilibrium exchange: concentrated suspensions of vesicles are equilibrated passively with radioactive lactose. Aliquots are then diluted into buffer with cold lactose (equimolar concentration). Right panel: typical time traces of efflux and exchange showing the effect of deuterium oxide at equivalent pH and pD 7.5. Efflux is shown as circles and exchange as squares. Time traces recorded in H2O are shown in blue color and data collected in deuterium oxide are shown in red color. (b) Schematics of counterflow experiment: concentrated suspensions of vesicles are equilibrated passively with substrate, and aliquots are diluted into buffer containing radioactively labeled substrate at a much lower concentration. Right panel: typical time traces of counterflow showing the effect of deuterium oxide (color coding is the same as in (a)). The bar on top of the plot indicates the extent of the two part-reactions, exchange (magenta) and efflux (green). The time traces in (a) and (b) are adapted from [37].
