Bacteriorhodopsin drives the glutamate transporter of synaptic vesicles after co‐reconstitution

Active accumulation of neurotransmitters by synaptic vesicles is an essential component of the synaptic transmission cycle. Isolated vesicles show energy‐dependent uptake of several transmitters by processes which are apparently mediated by a proton electrochemical potential across the vesicle membrane. Although this energy gradient is probably generated by a proton ATPase, the functional separation of ATP cleavage and transmitter uptake activity has only been shown clearly for monoamine transport. We report here that the light‐driven proton pump, bacteriorhodopsin, can replace the endogenous proton ATPase in proteoliposomes reconstituted from vesicular detergent extracts. The system shows light‐dependent uptake of glutamate with properties very similar to those observed in intact vesicles, e.g. chloride dependence or stimulation by NH4+. Our experiments show that the proton pump and the glutamate transporter are separate entities and provide a powerful tool for further characterization of the glutamate carrier.