Osmolyte

Osmolytes are low-molecular weight organic compounds that influence the properties of biological fluids.[1] Their primary role is to maintain the integrity of cells by affecting the viscosity, melting point, and ionic strength of the aqueous solution. 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 interact with the constituents of the cell, e.g. they influence protein folding.[3] Common osmolytes include amino acids, sugars and polyols, methylamines, methylsulfonium compounds, and urea.

Case studies

Natural osmolytes that can act as osmoprotectants include trimethylamine N-oxide (TMAO), dimethylsulfoniopropionate, 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]

References
  1. Paul H. Yancey (2005). "Organic osmolytes as compatible, metabolic and counteracting cytoprotectants in high osmolarity and other stresses". Journal of Experimental Biology. 208 (15): 2819–2830. doi:10.1242/jeb.01730. PMID 16043587.
  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. Arakawa T, Timasheff SN (1985). "The stabilization of proteins by osmolytes". Biophysical Journal. 47 (3): 411–414. Bibcode:1985BpJ....47..411A. doi:10.1016/s0006-3495(85)83932-1. PMC 1435219. PMID 3978211.
  6. Miller, AL; Elam, WA; Johnson, BH; Khan, SH; Kumar, R; Thompson, EB (2017). "Restored mutant receptor:Corticoid binding in chaperone complexes by trimethylamine N-oxide". PLOS One. 12 (3): e0174183. doi:10.1371/journal.pone.0174183. PMC 5354453. PMID 28301576.
  7. Csonka LN (1989). "Physiological and genetic responses of bacteria to osmotic stress". Microbiology and Molecular Biology Reviews. 53 (1): 121–147. PMC 372720. 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 2943332. 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 3970477. PMID 24591588.

Further reading


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