The serotonin transporter (SERT) is a sodium/chloride-dependent neurotransmitter transporter (NTT) belonging to the solute carrier 6 (SLC6) gene family. It is integrated into the membrane of neurons, with both the amino-/N- and carboxy-/C-terminus located in the cell lumen. Through structural rearrangements (i.e. conformational changes) SERT rapidly terminates neurotransmission via selective re-uptake of serotonin from the synaptic cleft. SERT is closely related to the transporters for norepinephrine (NET) and dopamine (DAT), with both of whom it forms the monoamine neurotransmitter transporter subfamily. All of which are of pharmaco-therapeutic relevance, as they are the target of many drugs, including antidepressants and (recreational) psychostimulants, such as amphetamine and cocaine. Upon amphetamine binding, SERT adopts a reversed function, to release serotonin into the cytoplasm. The N-terminus had been hypothesized to play a major role in the maintenance of amphetamine induced substrate efflux, and specific alterations in this region were found to change these properties. It is thought to act as a lever, allowing the first moiety of the SERT dimer to simultaneously promote efflux from the second one. To probe the conformational changes of SERTs N terminus upon amphetamine binding, in situ proteolysis studies were performed. Subsequent GFP fluorescence detection revealed the N-terminus was more susceptible to proteolytic cleavage when the transporter was in the inward-facing, as opposed to its outward-facing state. This result agrees with findings from truncation mutant experiments: Excluding the first 22 amino acids (construct SERT-N22) of the 85 amino acids comprising N-terminus did not impair efflux versus wildtype SERT. This was not true when at least 32 residues thereof (construct SERT-32) were removed. As for influx and inhibitor binding, different SERT mutants modified within the N-terminal region remained functional. Conversely, those constructs with mutations between residues 22 and 32 were crucial in promoting substrate release. Their substitution with alanine residues reduced substrate efflux by approximately 50 %. Further N-terminal truncation mutants were created and tested in terms of their functional activity, ligand binding and expression at the cell surface. Decreases in substrate efflux were exclusively observed in those SERT constructs with their N-termini shortened by 32 or 42 (constructs SERT-N32 and SERT-N42) amino acids, respectively. Using an additional electrophysiological approach, we examined the individual transporter cycle steps by recording ionic currents along wildtype and mutant SERT (SERT-N22 and SERT-N32). The steady state currents remained essentially unaffected regardless of the respective molecular background tested. However, a lower recovery rate of the capacitive peak indicated significant defects exclusively in cells expressing the SERT-N32 construct. These data suggest a selective impairment in the exchange mode of the SERT-N32 truncation mutant, thus, confirming the N-terminus lever behaviour enabling the switch between SERTs transport modes. To further localize underlying N terminal protein-protein interactions, the amber stop-codon (TAG) technology was utilised. To this end, the unnatural amino acid p-benzoyl phenylalanine (BzF), functioning as a photo-sensitive crosslinker, was inserted into the SERT region between the N-terminal residues 22 and 32. In principle, this approach enables localization of intra- and intermolecular protein interaction. However, methodological limitations rendered the results from these studies inconclusive. In summary, this studys findings suggest the N-terminus interacts with other regions in the SERT dimer and is essential for regulating the transporters amphetamine-induced efflux. As a likely unifying feature among all SLC6 family members, this mode of communication has been reported in the literature.