Further analysis of the difference between D20 and D14 truncations of the SERT C-terminus, which retained 0% compared to 90% transport rates, respectively, revealed the sequence Homatropine Bromide SITPET. Labetalol hydrochloride Within this region, there are 3 potential phosphorylation sites at S611, T613, and T616. Several studies have demonstrated that PKC modulators, such as bPMA, reduce SERT localization on the plasma membrane and blunt 5HT uptake capacity. Additionally, these studies also established an interaction of PP2A, a component of the protein phosphatase complex, with SERT. Based on these findings, we analyzed the effects of phosphorylation-mimicking amino acids on the 5HT uptake rate of SERT. Our results indicate that S611 may be a key site for phospho-regulation, since the single mutation of S611 to D caused a 61% decrease in 5HT uptake rate whereas the single mutation of S611 to A caused no reduction in 5HT uptake. T613 and T616 individually do not appear to be critical phospho-regulatory residues since neither mutation of T613 and T616 showed a similar level of 5HT uptake rate. However, it is possible that these sites work in conjunction with each other to modulate the function of the transporter since our results indicate that the triple mutation DDD of 611, 613, and 616 retained only 5% of its 5HT uptake capacity as compared to control SERT. It is also important to note that the presence of such a large amount of negative charge on the end of the protein could cause alterations in protein folding or proteinprotein associations that are important for protein function, resulting in the observed blunting of transport capacity. Next, we analyzed the impact of four truncations of the SERT C-terminus on the trafficking and expression of SERT on the plasma membrane using biotinylation and IF assays. Our data indicate that depending on the amount of truncation from the Cterminus of SERT, there was altered localization of the transporter. Therefore, we carried out a biotinylation analysis on some of the phosphorylation-mimicking mutations in an effort to determine the plasma membrane localization of these mutants, i.e., whether the mutation arrests them intracellularly or whether the mutants can still traffic to the plasma membrane. The data indicate that 3 possible phosphorylation sites do contribute to the 5HT uptake rates of transporters via inhibiting their proceedings toward the plasma membrane.