Amino acids serve both to nourish and as signalling molecules in cells and, consequently, so do their biomembrane transporters. In fact, some of these transporters may initiate signalling while transporting an amino acid substrate rather than serving simply to transport a signalling molecule. Most amino acid transporters now appear to have been cloned, and virtually all the cloned transporters are listed in solute carrier tables for easy access online. The characteristics of the transporters as they are expressed normally in cells do not always correspond to the characteristics of cloned transporters, however, and their transport and signalling functions will likely continue to emerge long after all transporters have been identified. For example, amino acids are metabolised to products that regulate DNA and specific epigenetic histone modifications in embryonic stem cells in order to maintain their proliferation and pluripotency. Alterations in these histone modifications may be expressed in a transgenerational manner and include both intracellular and extracellular histone actions.

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