Abstract
Apart from their pivotal roles in anabolic protein synthesis, cationic amino acids, particularly, L-lysine HCl and its oligomers, up to molecular weight 1000, showed a remarkable property of cellular growth stimulation both in vitro and in vivo. L- and D-Lysine HCl, at a maximal stimulatory concentration of 7 μg/mL of added load of the amino acid, supported a characteristic time-scaled cellular expansion in vitro, and L-lysine-mediated cell expansion in batch cultures always showed a stimulation index (S.I.) ranging up to ~35, compared with the matched control populations. Variable S.I. was possibly due to factors such as seeding density, type of media additives, number of passages the cells have undergone before being stimulated, etc. Beyond and before maximal stimulatory concentration of the amino acid, there is a sharp decline in the cellular growth-promoting activity of monomeric L-lysine HCl in vitro, thereby showing a clear concentration window for maximum cellular growth promotion. While the essential amino acid does not have any dedicated cell surface receptor, the monomeric and oligomeric amino acid molecule(s) possibly mediates the serum-derived growth factor-receptor binding on the cell membrane by having two cationic charge centres at two ends of the molecule. Beyond a cutoff molecular weight of 1000, oligomeric lysines did not show any positive effects on either cell division and secretion.
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