Glycerol activity

The low incorporation of [%[-glycerol into tumoral lipids would indicate a decrease of the glycerophosphate pathway for the glycerolipid biosynthesis. Nevertheless a lack in the glycerol activation to sn-glycerol-3-phosphate by the tumdral tissue cannot be ruled out. 

Storage Purified restriction enzymes are generally stored at — 20°C in buffers containing 50% glycerol. Activity loss can be further prevented by adding autoclaved gelatin or BSA to a final concentration of 50—100 fig/ml. Some enzymes (e.g., EcoRI and Pstl) are also stabilized by the presence of neutral detergents (e.g., 0.2% Triton X-100). 

HC CH(0H) CH20H. optically active. D-glyceraldehyde is a colourless syrup. May be prepared by mild oxidation of glycerol or by hydrolysis of glyceraldehyde acetal (prepared by oxidation of acrolein acetol). DL-glyceraldehyde forms colourless dimers, m.p. IBS-S C. Converted to methylglyoxal by warm dilute sulphuric acid. The enantiomers... 

Refining. The refining of natural glycerol is generally accompHshed by distillation, followed by treatment with active carbon. In some cases, refining is accompHshed by ion exchange (qv). 

Commercial production and consumption of glycerol has generaHy been considered a fair barometer of industrial activity, as it enters into such a large number of industrial processes. It generaHy tends to rise in periods of prosperity and faH in recession times. 

Starters. Nearly any compound having an active hydrogen can be used as starter (initiator) for the polymerization of PO. The common types are alcohols, amines, and thiols. Thus in Figure 2 ROH could be RNH2 or RSH. The fiinctionahty is derived from the starter, thus glycerol results in a triol. Some common starters are shown in Table 4. The term starter is preferred over the commonly used term initiator because the latter has a slightly different connotation in polymer chemistry. Table 5 Hsts some homopolymer and copolymer products from various starters. 

Microbiol Stability. Microbial growth is hindered by reducing water activity and adding preservatives. An overview is available (30). Reduction in water activity is typically obtained by including approximately 50% of a polyalcohol such as sorbitol or glycerol. Furthermore, 20% of a salt like NaCl has a pronounced growth inhibiting effect. 

The synthetic utihty of the above transformations stems from the fact that many monoesters obtained as a result of hydrolysis may be converted to pharmaceutically important intermediates. For example, the optically active glycerol derivative (27) is a key intermediate in the production of P-blockers. Akyl derivative (25) may be converted into (5)-paraconic acid [4694-66-0] ((5)-5-oxo-3-tetrahydrofurancarboxyhc acid) that is a starting material for the synthesis of (3R)-A-factor. The unsaturated chiral cycHc monoacetate (31) is an optically active synthon for prostaglandins, and the monoester (29) is used for the synthesis of platelet activating factor (PAF) antagonists. 

Surface-Active Agents. Polyol (eg, glycerol, sorbitol, sucrose, and propylene glycol) or poly(ethylene oxide) esters of long-chain fatty acids are nonionic surfactants (qv) used in foods, pharmaceuticals, cosmetics, textiles, cleaning compounds, and many other appHcations (103,104). Those that are most widely used are included in Table 3. 

Eicosanoids, so named because they are all derived from 20-carbon fatty acids, are ubiquitous breakdown products of phospholipids. In response to appropriate stimuli, cells activate the breakdown of selected phospholipids (Figure 25.27). Phospholipase Ag (Chapter 8) selectively cleaves fatty acids from the C-2 position of phospholipids. Often these are unsaturated fatty acids, among which is arachidonic acid. Arachidonic acid may also be released from phospholipids by the combined actions of phospholipase C (which yields diacyl-glycerols) and diacylglycerol lipase (which releases fatty acids). 

The metabolic breakdown of triacylglycerols begins with their hydrolysis to yield glycerol plus fatty acids. The reaction is catalyzed by a lipase, whose mechanism of action is shown in Figure 29.2. The active site of the enzyme contains a catalytic triad of aspartic acid, histidine, and serine residues, which act cooperatively to provide the necessary acid and base catalysis for the individual steps. Hydrolysis is accomplished by two sequential nucleophilic acyl substitution reactions, one that covalently binds an acyl group to the side chain -OH of a serine residue on the enzyme and a second that frees the fatty acid from the enzyme. 

Step 3 of Figure 29.3 Alcohol Oxidation The /3-hydroxyacyl CoA from step 2 is oxidized to a /3-ketoacyl CoA in a reaction catalyzed by one of a family of L-3-hydroxyacyl-CoA dehydrogenases, which differ in substrate specificity according to the chain length of the acyl group. As in the oxidation of sn-glycerol 3-phosphate to dihydroxyacetone phosphate mentioned at the end of Section 29.2, this alcohol oxidation requires NAD+ as a coenzyme and yields reduced NADH/H+ as by-product. Deprotonation of the hydroxyl group is carried out by a histidine residue at the active site. 

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