SMTP general structure, TP2 and derived TM9 peptide sequences, fluorophores studied here and cell uptake of dye-labeled TM9.(a) SMTP structural composition, TP2 precursor sequence as representative example and TM9 peptide sequence with ATTO 425 and TAMRA structures. (b) Confocal images of cells treated with increasing concentrations of TM9-ATTO 425 and TM9-TAMRA in free serum medium. Concerning the former, endocytic bright spots are detectable at 0.5 and 3 μM, while direct translocation is prevalent at 5 and 10 μM. Concerning the latter, only endocytosis is present at all the concentrations tested. Scale bars: 10 μm. (c) Confocal images of cells treated with 3 μM (left) and 10 μM (right) of TM9-ATTO 425 at 4 °C. While in the former case only cell plasma membranes are labelled (i.e. endocytosis is blocked), in the latter one diffuse cytoplasmic staining is still evident (i.e. direct translocation occurs).
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