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Osmolytes are compounds affecting osmosis.[1] They are soluble in the solution within a cell, or in the surrounding fluid, e.g. as plasma osmolytes. They play a role in maintaining cell volume and fluid balance. For example, when a cell swells due to external osmotic pressure, membrane channels open and allow efflux of osmolytes which carry water with them, restoring normal cell volume.[2] Osmolytes also contribute to protein folding.[3] Natural osmolytes that can act as osmoprotectants include trimethylamine N-oxide (TMAO), dimethylsulfoniopropionate, trimethylglycine, sarcosine, betaine, glycerophosphorylcholine, myo-inositol, taurine, glycine, and others.[4][5] Remarkably, TMAO has the capacity to restore glucocorticoid binding to mutant receptors. [6] Bacteria accumulate osmolytes for protection against a high osmotic environment.[7] The osmolytes will be neutral non-electrolytes, except in bacteria that can tolerate salts.[5] In humans, osmolytes are of particular importance in the renal medulla.[8] Current understanding of osmolytes have been used to calculate the maximum depth where a fish can survive: 26,900 feet (8,200 meters).[9]


  1. ^ "everythingbio.com". 
  2. ^ Review of Medical Physiology, William F. Ganong, McGraw-Hill Medical, ISBN 978-0-07-144040-0.
  3. ^ Bolen DW, Baskakov IV (2001). "The osmophobic effect: natural selection of a thermodynamic force in protein folding". Journal of Molecular Biology. 310 (5): 955–963. doi:10.1006/jmbi.2001.4819. PMID 11502004. 
  4. ^ Neuhofer, W.; Beck, F. X. (2006). "Survival in Hostile Environments: Strategies of Renal Medullary Cells". Physiology. 21 (3): 171–180. doi:10.1152/physiol.00003.2006. PMID 16714475. 
  5. ^ a b Arakawa T, Timasheff SN (1985). "The stabilization of proteins by osmolytes" (PDF). Biophysical Journal. 47 (3): 411–414. Bibcode:1985BpJ....47..411A. doi:10.1016/s0006-3495(85)83932-1. PMC 1435219Freely accessible. PMID 3978211. 
  6. ^ Restored mutant receptor: Corticoid binding in chaperone complexes by trimethylamine N-oxide. PMID: 28301576 PMCID: PMC5354453 DOI: 10.1371/journal.pone.0174183
  7. ^ Csonka LN (1989). "Physiological and genetic responses of bacteria to osmotic stress". Microbiology and Molecular Biology Reviews. 53 (1): 121–147. PMC 372720Freely accessible. PMID 2651863. 
  8. ^ Gallazzini, M.; Burg, M. B. (2009). "What's New About Osmotic Regulation of Glycerophosphocholine". Physiology. 24 (4): 245–249. doi:10.1152/physiol.00009.2009. PMC 2943332Freely accessible. PMID 19675355. 
  9. ^ Yancey PH, Gerringer ME, Drazen JC, Rowden AA, Jamieson A (2014). "Marine fish may be biochemically constrained from inhabiting the deepest ocean depths". PNAS. 111 (12): 4461–4465. Bibcode:2014PNAS..111.4461Y. doi:10.1073/pnas.1322003111. PMC 3970477Freely accessible. PMID 24591588. 

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