ABSTRACT
There are in excess of 800 amino acids found in nature. The consistent use of one or more of these select amino acids by so many taxa suggests that these amino acids have special characteristics compatible with their role in regulating cell volume. Many organisms maintain high concentrations of intracellular free amino acids to offset high osmolarity in the environment or extracellular fluid. The role of these solutes in cell volume regulation has been the subject of study and review for several decades. Essential amino acids are generally found in low concentration in cells and do not play a major role in cell volume recovery. Conservation of these amino acids for protein synthesis and other metabolic functions is undoubtedly a higher priority than simply using them as osmotically active solutes. The zwitterionic nature of amino acids makes them quite soluble in water, although the solubility of L-amino acids in pure water varies more than three orders of magnitude.
