Organic osmolytes

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. 

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... 

Application of fluid-state PC also initiates biochemical changes in cell cultures. Fluid-state PC increases cellular lipid fluidity and decreases the rate of proliferation of HaCaT human keratinocytes. No toxicity was observed.29 Choline, which is a metabolite of PC and the precursor of the organic osmolyte betaine, is actively transported to the keratinocytes. The relevance of this finding is not understood.30 Acetylcholine is synthesized, secreted, and degraded in human keratinocytes.31 In addition, PLD, which generates choline from PC, is involved in the differentiation of keratinocytes.32... 

N-methylglycine, an organic osmolyte with a nitric oxide scavenging action.41... 

The chemical properties that appear to underlie the fitness of the four classes of organic osmolytes include the following. First, these osmolytes are polar molecules that have high solubilities in water. They can be accumulated to high concentrations without unduly taxing the solvent capacity of the cell. Glycerol,... 

Figure 6.2. (Upper panel) The four major classes of organic osmolytes (I) sugars and polyhydric alcohols (polyols) (II) amino acids and amino acid derivatives (III) methylated ammonium and sulfonium compounds and (IV) urea. (Figure modified after Somero and Yancey, 1997.) (Lower panel) Structures of charged osmolytes accumulated in extremely halophilic archaea (after Martin et al., 1999). Note that these osmolytes commonly represent a type of organic osmolyte that is found in many bacteria or eukaryotes to which a charged group has been attached. Typically, the charged group is anionic, for example, a phosphate or a carboxylate group.

To develop an understanding of the rationales underlying the selection of the particular types of organic osmolytes found in cells, it is appro-... 

Compatibility of Organic Osmolytes with Biochemical Systems ... 

Figure 6.5. Compatibility of organic osmolytes with enzyme function. (Upper panel) Pyruvate kinase of the marine crab Pachygrapsus crassipes. The effects of KC1 and NaCI and several organic solutes on the Km of phosphoenol pyruvate (PEP) (modified after Bowlus and Somero, 1979). (Middle panel) Malate dehydrogenase of the mangrove (Rhizophora mangle). Effects of NaCI and three organic osmolytes (the amino acid proline and the polyols pinitol and OMMI) on catalytic activity (modified after Sommer et al., 1990). (Bottom panel) Effects of NaCI and four osmolytes found in mammalian kidney (urea, glycine betaine, sorbitol, and inositol) on the Km of uric acid of uricase (modified after Yancey, 1992). (Figure modified after Somero and Yancey, 1997.)...

Figure 6.8. The effects of four organic osmolytes, glycerol, sarcosine, glycine betaine, and TMAO on salt-inhibited ribulose-1,5-bisphosphate-carboxylase-oxygenase (RuBisCO) activity of the cyanobacterium Aphanothece halophytica. The enzyme was placed in a solution containing KC1 at a concentration sufficient to inhibit activity by 50%. Then, increasing concentrations of organic osmolytes were added to the assay medium, leading to restoration of activity. (Modified after Incharoensakdi et al., 1986.)...

Analysis of the physical-chemical principles underlying selection of organic osmolytes— and combinations thereof—involves a logically linked series of why questions. We have already addressed one why question above,... 

A third mechanism involves charge repulsion between protein and cosolvent. The fact that most organic osmolytes lack a net charge suggests that this mechanism is of less general significance than the effects of surface tension and steric hindrance. 

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