Hydrophobic metabolites

These have been effectively used to remove lignin and hydrophobic metabolites from plant-derived samples. Bonded-phase mini-columns are also ideal for the prechromatographic purification of a perbenzoylated sugars, glycopeptides (and derived oligosaccharides), and peralkylated oligosaccharides. ... 

Serum albumin is a natural transporter of hydrophobic metabolites it binds toxic ligands reversibly, and if the ligand can be removed from the complex then the melting curve of unloaded albumin should return to that of pure protein. However this remains a difficult task, and neither exhaustive dialysis, nor the use of conventional carbonic sorbents, influence the shape of melting curves of albumin isolated from blood plasma of uremic patients and patients with hepatic insufficiency (Fig. 29.3) [9]. 

There are five intracellular retinoid binding proteins that show considerable sequence homology not only with each other, but also with a variety of other intracellular binding proteins for hydrophobic metabolites, including the intracellular fatty acid binding protein (Li and Norris, 1996 Noy, 2000 Vogel et al., 2001). 

Our standard separation procedure consists of defatting dried plant material with petroleum ether and extraction with solvents of increasing polarity CHCI3, CHCl3-MeOH, MeOH, H2O thus hydrophobic metabolites are found in the CHCI3 extract and glycosides in the CHCl3-MeOH, MeOH and H2O extracts. 

The same group showed that e-allylselenocysteine (98), which is expected to yield allylselenol, a fairly hydrophobic metabolite, has more anti-carcinogenic power than 77 and propylselenocysteine (99) in rat methylnitrosourea model [233]. The diallyl selenide (106) has significant anti-carcinogenic activity using DMB-induced mammary tumor model and is 300 times more active than the diallyl sulfide, a flavor component of garlic [234]. 

Even when adopting a targeted approach, the coverage of lipids in a specific class can still be restricted by the dominance of a few very abundant lipids. This may be the case for steroid analysis where cholesterol is often the most abundant steroid by two orders of magnitude. This problem can be minimized by subdivision of the steroid class according to hydropho-bicity where cholesterol and more hydrophobic steroids represent one class, and oxysterols (oxidized forms of cholesterol and its precursors) and less hydrophobic metabolites represent a second class [45]. This is an approach we adopted for the analysis of steroid sulphates and bile acid/ alcohol conjugates by shotgun steroidomics, and in our LC-ESl-MS/MS work on oxysterols and cholestenoic acids in brain [46,47], plasma [48], and cerebrospinal fluid (CSF) [49]. 

Separation media, with bimodal chemistry, are generally designed for the complete separation of complex samples, such as blood plasma serum, that typically contain molecules differing in properties such as size, charge, and polarity. The major principle of bifunctional separation relies on the pore size and functional difference in the media. For example, a polymer bead with hydrophilic large pores and hydrophobic small pores will not interact with and retain large molecules such as proteins, but will interact with and retain small molecules such as drugs and metabolites. 

Many of the phase 1 enzymes are located in hydrophobic membrane environments. In vertebrates, they are particularly associated with the endoplasmic reticulum of the liver, in keeping with their role in detoxication. Lipophilic xenobiotics are moved to the liver after absorption from the gut, notably in the hepatic portal system of mammals. Once absorbed into hepatocytes, they will diffuse, or be transported, to the hydrophobic endoplasmic reticulum. Within the endoplasmic reticulum, enzymes convert them to more polar metabolites, which tend to diffuse out of the membrane and into the cytosol. Either in the membrane, or more extensively in the cytosol, conjugases convert them into water-soluble conjugates that are ready for excretion. Phase 1 enzymes are located mainly in the endoplasmic reticulum, and phase 2 enzymes mainly in the cytosol. 

Buprofezin and its metabolites, p-OH-buprofezin and BF12, are hydrophobic under neutral conditions. Having the organic base part in their chemical structure, these compounds form water-soluble salts under strongly acidic conditions. The change in solubilities of these compounds influences the cleanup procedure. Four different residue analytical methods have been developed to measure buprofezin and its metabolites in plants (rice, citrus and tomato cucumber, pepper, tomato, squash and eggplant), soil and water ... 

As in the other -omics, analyses may be directed at a specific metabolite, at all metabolites in a given system in a shot-gun approach, or at accessible groups of molecules in profiling experiments. In that also the technology varies. In addition, the chemistry of different metabolites is very heterogeneous since it involves hydrophobic lipids, hydrophilic carbohydrates, ionic inorganic species, and other secondary natural products and already the choice of solvent in metabolite extraction dictates which types of molecules will be present (Fig. 10.8). Therefore, total metabolome profiling is not possible, because no analytical method will be able to accommodate all the different molecule classes at once. 

These points, however, do not address the central question of how organisms deal with a contaminated environment with which they have to interact in order to obtain energy and metabolites. Crucial to these processes are the cellular processes which can modify the ionisation of molecules, their hydrophilic/ hydrophobic properties, and the matrix within which they exist. Many of these changes occur in the alimentary tract but they also occur at the cellular... 

An interesting vertical profile of the metabolite concentrations was observed the compounds showed a tendency to accumulate at the two-phase boundaries of air-freshwater and freshwater-saline water (the halocline). Thus, concentration maxima were observed at depths of 0 and 2 m (see Fig. 6.4.1) [6]. The observed distribution may result from either the physicochemical properties of these compounds (surface activity and hydrophobicity), or their formation at the interface due to increased biological activity. For the parent surfactants a similar but less pronounced vertical distribution pattern was observed (with maxima at 0 and 2 m of 17 and 9 xg L 1, respectively) [5],... 

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