ABSTRACT
Guanidinium Ions and Fatty Acids ...................................................... 354
20.3 The Importance of Bidentate Hydrogen Bonding in Adaptive
Partitioning and Cellular Uptake .......................................................... 356
20.4 Counter Ions of Guanidinium-Rich Transporters Are
Exchanged at the Cell Surface .............................................................. 358
20.5 Role of Membrane Potential in Transporter Translocation .................. 359
20.6 Quantitative Measurement of Uptake and Release of a
Luciferin Prodrug in Cells .................................................................... 362
20.7 Discussion and Conclusions .................................................................. 367
Acknowledgments ............................................................................................ 370
References ........................................................................................................ 371
Biological membranes have evolved in part to prevent biopolymers and polar
molecules from passively entering cells.1 Numerous organisms have developed
proteins, many of which are transcription factors, that breach these biological
barriers through a variety of mechanisms.2 The protein HIV Tat, for example, when
used in vitro, rapidly enters the cytosol (and nucleus) of a wide spectrum of cells
after endocytosis.3 However, the nine amino acid peptide required for the uptake of
HIV Tat, residues 49-57 (RKKRRQRRR), appears itself to utilize an additional
mechanism as evident from its uptake, even at 48C, by a route differentiated from the
intact protein.4 We have found that guanidinium-rich oligomers enter suspension
cells more effectively than the Tat nonamer,5 often without the production of
observable endocytotic vesicles.6,7 We describe herein studies on the cellular
uptake mechanism of guanidinium-rich transporters conjugated to small molecules
(MW ca.!3000). Pertinent to the formulation of a mechanism, our previous studies demonstrated
that the guanidinium head groups of Tat 49-57 are critical for its uptake into cells.
