Osmolyte

Yancey, P.H., Clark, M.E., Hand, S.C., Bowlus, R.D. Somero, G.N. (1982). Living with water stress. Evolution of osmolyte systems. Science, 217,1214-22. 

Proline, however, is the predominant amino acid and most interestingly, its betalamic acid adduct indicaxanthin is the major betalain pigment in cactus pear. Proline functions as an osmolyte, accumulating in water- and heat-stressed plant tissues, and in comparison to other amino acids, it exhibits an extraordinarily high solubility of 1623 mg/L water at 25°C. ... 

Interest in the possible persistence of aliphatic sulfides has arisen since they are produced in marine anaerobic sediments, and dimethylsulfide may be implicated in climate alteration (Charlson et al. 1987). Dimethylsnlfoniopropionate is produced by marine algae as an osmolyte, and has aronsed attention for several reasons. It can be the source of climatically active dimethylsulfide (Yoch 2002), so the role of specific bacteria has been considered in limiting its flux from the ocean and deflecting the prodncts of its transformation into the microbial sulfur cycle (Howard et al. 2006). 

Osmolytes in the Deep. Professor Paul H. Yancey, Whitman University,... 

DMSP (21) is produced by many marine micro- and macroalgae and is especially prominent in dinoflagellates and haptophytes. The nontoxic DMSP (21) fulfills multiple cellular functions including cryoprotection, the involvement as osmolyte in osmoregulation and as a methyl donor in transmethylation reactions [18]. 

An inherent property of osmolytes is that they lower the freezing point depressions of cells (Kirst 1996). Therefore, DMSP may also be acting as a cryoprotectant in algae exposed to freezing temperatures. However, Kirst (1996) argues that cellular concentrations of DMSP are too low to produce a significant freezing point depression. 

Nishiguchi MK, Somero GN (1992) Temperature- and concentration-dependence of compatibility ofthe organic osmolyte P-dimethylsulfoniopropionate. Cryobiology 29 118-124 Noordkamp D, Gieskes W, Gottschal J, Forney L, van Rijssel M (2000) Acrylate in Phaeocystis colonies does not affect surrounding bacteria. J Sea Res 43 287-296 Otte ML, Morris JT (1994) Dimethylsulphoniopropionate (DMSP) in Spartina altemiflora Loisel. Aquat Bot 48 239-259... 

Other physiological functions of MAAs in phototrophic organisms such as organic osmolytes have been suggested, because very high concentrations can be found in cyanobacteria living in hypersaline environments (Oren 1997). However, salt shock experiments with the marine cyanobacterium Microcoleus chthono-plastes did not indicate ary major involvement of MAAs in the process of osmotic acclimation (Karsten 2002), and hence their proposed function as osmolytes has to be questioned. 

Chen, B.L. and T. Arakawa. 1996. Stabilization of recombinant human keratinocyte growth factor by osmolytes and salts. J Pharm Sci 85 419-426. 

Within organisms, organic sulfur is present predominantly as the amino acids cysteine and methionine, and the algal and bacterial osmolyte, dimethylsulfoniopropionate (DMSP). The latter also serves as an antioxidant and cryoprotectant. Small amounts of organosulfur are also present in some polysaccharides, lipids, vitamins, enzymes, and in the iron-sulfur protein ferrodoxin. Cell lysis and microbial degradation releases... 

Osmolyte A neutral solute that reacts minimally with the contents of the ceU. It serves to protect cells from drying out and/or in responding to salinity changes. 

Miller TJ, Hanson RD, Yancey PH (2000) Developmental changes in organic osmolytes in prenatal and postnatal rat tissues. Comp Biochem Physiol A Mol Integr Physiol 125(l) 45-56 Naqvi NH, Rudrauf D, Damasio H, Bechara A (2007) Damage to the insula disrupts addiction to cigarette smoking. Science 315(5811) 531-534... 

The most superficial layer of skin is the stratum comeum (SC), which consists of terminally differentiated keratinocytes (comeocytes) that originate from actively proliferating keratinocytes in lower epidermis (basale, spinosum, and granulosum cells), and contain a lamellar lipid layer secreted from lamellar bodies (Fig. 7a). Flydration of the SC is an important determinant of skin appearance and physical properties, and depends on a number of factors including the external humidity, and its structure, lipid/protein composition, barrier properties, and concentration of water-retaining osmolytes (natural moisturizing factors, NMFs) including free amino acids, ions, and other small solutes. 

One group of kosmotropic stabilizers of proteins are the osmolytes, organic osmoprotectant solutes, mostly polyhydric alcohols and amino acids or their derivatives. Osmolyte compatibility of organisms is thought to result from absence of osmolyte interactions with substrates and cofactors, and the non-perturbing or favorable effects on macromolecular-solvent interactions (Yancey, 1982). 

A study of two of the most prominent and widespread osmolytes, betaine and beta-hydroxyectoine, by differential scanning calorimetry (DSC) on bovine ribonu-clease A (RNase A) revealed an increase in the melting temperature Tm of RNase A of more than 12 K and of protein stability AG of 10.6 kj mol-1 at room temperature at a 3 M concentration of beta-hydroxyectoine. The heat capacity difference ACp between the folded and unfolded state was significantly increased. In contrast, betaine stabilized RNase A only at concentrations less than 3 M. When enzymes are applied in the presence of denaturants or at high temperature, beta-hydroxyectoine should be an efficient stabilizer. 

S. Knapp, R. Ladenstein, and E. A. Galinski, Extrinsic protein stabilization by the naturally occurring osmolytes beta-hydroxyectoine and betaine, Extremophiles 1999, 3, 191-198. 

I. M. Plaza del Pino and J. M. Sanchez-Ruiz, An osmolyte effect on the heat capacity change for protein folding, Biochemistry 1995, 34, 8621-8630. 

R. D. Bowlus, and G. N. Somero, Living with water stress evolution of osmolyte systems, Science 1982, 237, 1214-1222. 

K. D. Collins. Ions from the Hofmeister series and osmolytes Effects on proteins in solution and in the crystallization process. Methods, 34(3) 300-311, 2004. 

---