hide
Free keywords:
Halorhodopsin; Black lipid membrane; Photocurrent; Chloride transport
Halide transport; (H. halobium)
Abstract:
Halorhodopsin-containing membrane fragments were isolated from Halobacterium halobium strain L-33, a bacteriorhodopsin-deficient mutant. When these so called Tween-washed membrane fragments are added to one side of a positively charged planar lipid bilayer the system becomes photoelectrically active. Under stationary light conditions photocurrent transients are obtained while the steady-state photocurrent is extremely low. The steady-state photocurrent, however, is considerably increased when the lipid bilayer is doped with the Cl−/OH− exchanging carrier triphenyltin together with a proton carrier. These results suggest that halorhodopsin is associated with the underlying black lipid membrane in a sandwich-like structure. The photoresponse occurs only in the presence of Cl−, Br− and I− with half-saturation concentrations in the range of 1–10 mM and is virtually independent on the type of the cation (Na+, K+, Mg2+) present. With other anions, such as SO4−2, F−and NO3− no photoresponse was obtained. The results provide direct evidence that halorhodopsin is a light-driven electrogenic pump with a high specificity for halides.
