Enzyme lipase, triacylglycerol

This enzyme [EC 3.1.1.34] (also called clearing factor lipase, diglyceride lipase, and diacylglycerol lipase) catalyzes the hydrolysis of a triacylglycerol to produce a diacylglycerol and a fatty acid anion. This enzyme hydrolyzes triacylglycerols in chylomicrons and in low-density lipoproteins and also acts on diacylglycerols. See also Lipases... 

Among enzymes, lipases proved to be the most efficient for the in vitro polyester synthesis. Lipases or triacylglycerol acylhydrolases are water-soluble enzymes that catalyze the hydrolysis of ester bonds in water-insoluble, lipid substrates, and therefore comprise a subclass of the esterases. 

Lipases (triacylglycerol hydrolases, EC 3.1.1.3) are enzymes that catalyze reactions such as hydrolysis, interesterification, esterification, alcoholysis, acidolysis, and aminolysis [1]. There is an increasing interest in the development of lipase applications to oleochemical transformations to obtain esters of long-chain fatty acids, as monoalkyl esters of fatty acids [2]. Utilization of lipase as a catalyst for the production of biodiesel, defined as a mixture of monoalkyl esters, is a clean technology due to its nontoxic and environmental fnendly nature, requiring mild operating conditions compared with chemical method [3]. 

Triacylglycerols are hydrolysed by lipolytic enzymes (lipases) in a step-wise fashion ultimately to yield glycerol and long chain fatty acids. In S. cerevisiae, lipase action is located in the plasma membrane [70]. Phospholipid hydrolysis is catalysed by phospholipases yielding glycerol and fatty acids, as well as products such as choline etc. Glycerol may be phosphorylated, oxidized and enter the EMP pathway as dihydroxyacetone phosphate. The long chain fatty acids are presumed to be converted to acetyl CoA by the p-oxidation pathway (Fig. 17.17). This pathway may be located either within the mitochondria or microbodies. 

Three forms of enzymic action relating to soybeans were identified by Ong (1980). Lipolytic enzymes (lipases) are responsible for the hydrolysis of triglycerides (triacylglycerols), thus increasing the free... 

Contrary to these processes, enzyme-catalyzed reactions using lipases have proven to be an interesting alternative for industrial-scale biodiesel production in order to reduce production costs. Lipases (triacylglycerol acyl-hydrolases, E.C. 3.1.1.3.) are powerful tools that can catalyze not only hydrolysis but also various synthetic reactions including esterification and transesterification. 

Lipase (triacylglycerol acylhydrolase, EC 3.1.1.3) is an enzyme that catalyzes the hydrolysis of a fatty acid glycerol ester in vivo by bond cleavage however, it was disclosed that lipase catalyzes a polymerization reaction to give polyesters... 

Barley grains contain a relatively low amount of lipid (up to 4.8 %), mainly present in the embryo and aleurone. Most of the lipids are stored as triacylglycerols. Lipase (triacylglycerol acylhydrolase [EC 3.1.1.3]) is the first enzyme involved in the degradation of stored triacylglycerols and has been studied extensively in oil-rich seeds [1] and in cereals such as oats, which contain relatively high levels of activity [2]. Less attention has been paid to wheat [3] and barley [4,5], which contain low levels of lipase activity. 

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. 

Figure 7.4 Fate of triacylglycerol that is present in fuel blood after secretion by the intestine. The dietary triacylglycerol in the intestine is hydrolysed to long-chain fatty acids and monoacyl-glycerol, both of which are taken up by the enterocytes in which they are then re-esterified. The triacylglycerol is released in the form of chylomicrons into the blood, from where it is hydrolysed to fatty acids and glycerol by the enzyme lipoprotein lipase in specific tissues (Figure 7.3). The fatty acids are taken up by adipocytes, muscle fibres and secretory cells in the mammary gland.

The physiological pathway for oxidation of fatty acids in organs or tissues starts with the enzyme triacylglycerol lipase within adipose tissue, that is, the hormone-sensitive lipase. This enzyme, plus the other two lipases, results in complete hydrolysis of the triacylglycerol to fatty acids, which are transported to various tissues that take them up and oxidise them by P-oxidation to acetyl-CoA. This provides a further example of a metabolic pathway that spans more than one tissue (Figure 7.13) (Box 7.1). 

During lactation, the enzyme is active in mammary gland and the released fatty acids are taken up and used to synthesise triacylglycerol for the milk. A few days before parturition, in preparation for lactation, the activity of lipoprotein lipase is increased in the mammary gland. 

Triacylglycerol Upases [EC 3.1.1.3] (also known as triglyceride lipases, tributyrases, or simply as lipases) catalyze the hydrolysis of a triacylglycerol to produce a diac-ylglycerol and a fatty acid anion. The pancreatic enzyme acts only on an ester-water interface the outer ester links in the substrate are the ones which are preferentially... 

Lipases are enzymes that catalyze the in vivo hydrolysis of lipids such as triacylglycerols. Lipases are not used in biological systems for ester synthesis, presumably because the large amounts of water present preclude ester formation due to the law of mass action which favors hydrolysis. A different pathway (using the coenzyme A thioester of a carboxylic acid and the enzyme synthase [Blei and Odian, 2000]) is present in biological systems for ester formation. However, lipases do catalyze the in vitro esterification reaction and have been used to synthesize polyesters. The reaction between alcohols and carboxylic acids occurs in organic solvents where the absence of water favors esterification. However, water is a by-product and must be removed efficiently to maximize conversions and molecular weights. 

Hydrolysis of triacylglycerols is catalyzed by lipoprotein lipase, a membrane-bound enzyme located on the endothelium lining the capillary beds of the muscle and adipose tissue. 

In the capillaries of these tissues, the extracellular enzyme lipoprotein lipase, activated by apoC-II, hydrolyzes triacylglycerols to fatty acids and glycerol (step... 

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