Effect of temperature on the function of a proton pump

Summary

Vesicles with proton translocating activity were reconstituted with bacterial rhodopsin lipoprotein and synthetic phospholipids. Reconstitution with dimyristoyl phosphatidylcholine yielded vesicles which catalyzed light-driven proton uptake which was sensitive to nigericin, gramicidin or an uncoupler when tested at temperatures above 20°C. At temperatures below 5°C, the extent of proton uptake was actually greater than at 20°C, but there was little effect of either nigericin or uncouplers even when these compounds had been added at 20°C. Gramicidin inhibited at all assay temperatures provided it was added at 20°C. With dipalmitoyl phosphatidylcholine similar results were obtained except that nigericin lost its effectiveness at higher temperatures. On illumination tetraphenylboron was taken up by the reconstituted vesicles. We propose that an electrogenic proton translocation takes place by a channel mechanism.