Lipids hydrolyzable

Figure 3. IR spectra of Lipid 1, (a) monomeric lipid, (b) After UV irradiation, (c) hydrolyzed lipid.

The components of the hydrolyzable lipids are linked to one another by ester bonds. They are easily broken down either enzymatically or chemically. 

Various pancreatic enzymes hydrolyze lipids, including lipase with its auxiliary protein colipase (see p. 270), phospholipase A2, and sterol esterase. Bile salts activate the lipidcleaving enzymes through micelle formation (see below). 

Hydrolases carry out important degradative reactions in the body. During digestion, lipases hydrolyze lipids and proteases convert protein to amino acids. Hydrolases cleave large molecules into fragments used for synthesis, the excretion of waste materials, or as sources of carbon for the production of energy. In these reactions, many biopolymers are converted to monomers. Some hydrolases release energy as they act. 

Enzymes that hydrolyze lipids are present in various tissues. Certain of these are activated by organic solvents, and the rate of activation increases as the solvent is warmed. At least one such enzyme is active in an ether dispersion. Thus, consideration must be given to the possibility of enzymatic degradation, particularly when dealing with plant sources. 

Hydrolyzable lipids can be cleaved into smaller molecules by hydrolysis with water. 

Most hydrolyzable lipids contain an ester unit. We will examine three subgroups waxes, triacylglycerols, and phospholipids. 

Waxes are the simplest hydrolyzable lipids. Waxes are esters (KCOOR ) formed from a h h molecular weight alcohol (R OH) and a fatty acid (RCOOH). 

Phospholipids are hydrolyzable lipids that contain a phosphorus atom. There are two common types of phospholipids phosphoacylglycerols and sphingomyelins. Both classes are found almost exclusively in the cell membranes of plants and animals, as discussed in Section 3.7. 

Figure 29.4 compares the structural features of the most common hydrolyzable lipids a triacyl-glycerol, a phosphoacylglycerol, and a sphingomyelin. 

Phospholipid (Sections 3.7A, 29.4) A hydrolyzable lipid that contains a phosphorus atom. 

Wax (Sections 4.15, 29.2) A hydrolyzable lipid consisting of an ester formed from a high molecular weight alcohol and a fatty acid. 

Lipids are categorized into hydrolyzable saponifiable) and nonhydrolyzable (nonsaponifiiable) lipids. Hydrolyzable lipids contain at least one ester group, which undergoes hydrolysis in the presence of an acid, a base, or an enzyme. Hydrolysis by base is referred to as saponification. Hydrolysis cleaves a saponifiable lipid into two or more smaller molecules. Nonhydrolyzable lipids do not undergo hydrolytic cleavage into smaller molecules. 

Problem 19.29. The answer to Problem 19.28 appears to be incorrect for leukotriene D. The side group in leukotriene D contains an amide group and amide groups do undergo hydrolysis. Should leukotriene D be classified as an hydrolyzable lipid ... 

This is an example of absolute specificity, the catalyzing of the reaction of one and only one substance. Other enzymes display relative specificity by catalyzing the reaction of structurally related substances. For example, the lipases hydrolyze lipids, proteases split up... 

Ethyl acetate is produced by the yeast, Saccharomyces cerevisiae, using the acetyl alcohol transferase enzyme. It links the acetate from the acetyl-coA with an ethanol molecule. The esters produced can be affected by esterases enzymes, because they hydrolyze the aliphatic and aromatic esters. These enzymes can hydrolyze lipids to obtain medium chain fatty acids (Moreno. 2009). Production of esters is related to the quantity of amino acids. When the nitrogen from the amino acids is high, fatty acids decrease and acyl transferase is not inhibited (Arrizon. 2001). 

In the United States, the total fat is defined as the total fatty acids expressed as triacylglycerols. Therefore, procedures for releasing fatty acids for total fat determination may be applicable to analysis of fatty acids per se. In the Association of Official Analytical Chemists (AOAC) official method 996.06 (AOAC, 1995), the sample is digested either with hydrochloric acid, to hydrolyze lipids and also carbohydrate and protein with which hpid material may be associated with, or with ammonia for dairy products, in the presence of an internal standard (triundecanoin). The fatty acids are then extracted with a petroleum ether-diethyl ether solvent mixture. As pointed out by Ackman (1999), the potential drawback of using hydrochloric acid is that not all hpids may be hydrolyzed totally to FFA. Presumably, this does not matter if an appropriate fatty acid derivatization procedure for FFA and esterified fatty acids (EFA) is subsequendy employed (see Section 2.3.3.1), as long... 

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