Osmolytes structures

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. 

The most commonly used generic term for a dissolved substance is solute, and this is the term that we will employ in most contexts, for both large and small compounds, that is, for macromolecules and micromolecules. A closely related term, cosolvent, is often used by physical chemists when the issue in question involves a dissolved substance that either stabilizes or destabilizes the structures of macromolecules. For instance, cosolvent is often used in literature on the effects of solutes on protein stability. A more restrictive and specific term that will be employed when we discuss the osmotic relationships of organisms is osmolyte. 

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.

OSMOLYTE COMPATIBILITY WITH MACROMOLECULAR STRUCTURE AND FUNCTION... 

Counteraction by methylamine osmolytes of salt perturbation of enzymatic activity, structures of contractile proteins, force development... 

The effects of solutes on distributions of microstates are analogous in important ways to the effects of changes in temperature (figure 6.13). A structure-stabilizing osmolyte like TMAO will favor compact, stable microstates. In the presence of a stabilizing cosolvent, the ensemble of configurational states thus includes a relatively small fraction of molecules whose... 

It can be seen in Fig. 9.8 that the transition shifts, as expected, to higher temperature as a function of increasing osmolyte concentration. The AV decreases in absolute value from —19 to —5 ml mol-1. This is in part due to the increase in the transition temperature, and because of a positive Aa (see Fig. 9.5) the volume between the unfolded and folded state decreases in absolute value. There may be a contribution of the effect of the osmolyte to the structure of the unfolded state as well. The value of a at low temperature increases with increasing osmolyte as a result of the preferential hydration effect. At high temperature, the differences in the expansivity of the bulk water... 

Viadiu H, Aggarwal AK. Structure of BamHI bound to nonspecific DNA a model for DNA sliding. Molec. Cell 2000 5 889-895. Sidorova NY, Muradymov S, Rau DC. Trapping DNA-protein binding reactions with neutral osmolytes for the analysis by gel mobility shift and self-cleavage assays. Nucleic Acids Res. 2005 33 5145-5155. 

It is still not clear why arsenobetaine should occur at such high levels in marine animals relative to freshwater and terrestrial animals. The structural similarity of arsenobetaine to the important osmolyte glycine betaine suggests that it may be utilized in some osmotic role within marine animals (18). 

Figure 1 Molecular structure of the osmolyte glycine betaine and its analog arsenobetaine.

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