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. 2017 Oct 12;7:13056. doi: 10.1038/s41598-017-13290-7

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© The Author(s) 2017

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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LacY transport activity in vesicles of different lipid composition. (A) LacY was reconstituted into vesicles with the enzyme β-galactosidase encapsulated. The substrate ο-NPG was added externally, with and without a pH gradient to measure active transport and facilitated diffusion respectively. Transported ο-NPG was digested to produce nitrophenol which was monitored by the increase in absorbance at 410 nm. (B) LacY reconstituted into 0.2/0.6/0.2 (mole fraction) DOPC/DOPE/DOPG vesicles showed a large increase in substrate transport in the presence of a pH gradient (black) over no gradient (green). (C) Diagrammatic representation of the transport activity of reconstituted LacY in vesicles composed of DOPC, DOPE and DOPG mixtures, comparing active transport to facilitated diffusion by the relative increase in initial velocity in the presence versus the absence of a pH gradient.