Bosshart PD Fotiadis D 2019 Transport of solutes across biological membranes is essential for cellular life. This process is mediated by membrane transport proteins which move nutrients, waste products, certain drugs and ions into and out of cells. Secondary active transporters couple the transport of substrates against their concentration gradients with the transport of other solutes down their concentration gradients. The alternating access model of membrane transporters and the coupling mechanism of secondary active transporters are introduced in this book chapter. Structural studies have identified typical protein folds for transporters that we exemplify by the major facilitator superfamily (MFS) and LeuT folds. Finally, substrate binding and substrate translocation of the transporters LacY of the MFS and AdiC of the amino acid-polyamine-organocation (APC) superfamily are described. https://sonar.ch/global/documents/293001 eng info:eu-repo/semantics/altIdentifier/doi/10.1007/978-3-030-18768-2_9 info:eu-repo/semantics/altIdentifier/pmid/31214990 Sub-cellular biochemistry. - 2019 Alternating access model Amino acid-polyamine-organocation superfamily Major facilitator superfamily Membrane transporter Secondary active transporter Transport mechanism Transporter fold Amino Acid Transport Systems Biological Transport Membrane Transport Proteins Secondary Active Transporters. http://purl.org/coar/resource_type/c_6501