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Lactate efflux-induced electrical potential in membrane vesicles of Streptococcus cremoris.

By R Otto, R G Lageveen, H Veldkamp and W N Konings


We developed a procedure for isolating membrane vesicles from the homolactic fermentative bacterium Streptococcus cremoris. The membrane vesicles were shown to have a right-side-out orientation by freeze-etch electron microscopy and to be free of cytoplasmic constituents. The membrane vesicles retained their functional properties and accumulated the amino acids L-leucine, L-histidine, and L-alanine in response to a valinomycin-induced potassium diffusion gradient. Studies with these membrane vesicles strongly supported the possibility that there was a proton motive force-generating mechanism by end product efflux (Michels et al., FEMS Lett. 5:357-364, 1979). Lactate efflux from membrane vesicles which were loaded with L-lactate and diluted in a lactate-free medium led to the generation of an electrical potential across the membrane. The results indicate that lactate efflux is an electrogenic process by which L-lactate is translocated with more than one proton

Topics: Research Article
Year: 1982
OAI identifier: oai:pubmedcentral.nih.gov:216566
Provided by: PubMed Central
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