BH3 peptides bind their targets inside the cell, but an unmodified peptide of this size does not cross the plasma membrane. This product addresses that by fusing the BID BH3 sequence to an octaarginine cell-penetrating tag. Comparing the supplied molecular weights across this series, it differs from the nonaarginine version (LT1053) by approximately 156, which corresponds to a single arginine residue. Polyarginine tags enter cells through a combination of direct translocation and endocytic uptake, and uptake efficiency depends on the number of arginines rather than increasing indefinitely with length. Work comparing polyarginine peptides with cargoes has examined how chain length and the attached cargo together determine delivery, which is precisely why both the R8 and R9 forms of this peptide are offered: the optimum is system-dependent and is usually established empirically. The BID BH3 cargo itself acts as an activator of BAK and BAX, so a successful delivery is expected to register as apoptosis rather than as a silent uptake event. Two cautions apply when interpreting results. Endosomal entrapment means measured uptake does not always equal cytosolic availability, so a functional readout is more informative than fluorescence alone. And highly cationic peptides can perturb membranes at higher concentrations independently of their cargo, so a polyarginine-only control at matched concentration is worth including. | 