Triglycerides, lipase-catalyzed

The steps in the subsequent utilization of muscle LCFAs may be summarized as follows. The free fatty acids, liberated from triglycerides by a neutral triglyceride lipase, are activated to form acyl CoAs by the mediation of LCFAcyl-CoA synthetase which is situated on the outer mitochondrial membrane. The next step involves carnitine palmitoyl transferase I (CPT I, see Figure 9) which is also located on the outer mitochondrial membrane and catalyzes the transfer of LCFAcyl residues from CoA to carnitine (y-trimethyl-amino-P-hydroxybutyrate). LCFAcyl... 

H. Uzawa, Y. Nisbida, H. Ohrui, H. Meguro, A New Approach to Determine the Stereospecificity in Lipase Catalyzed Hydrolysis Using Circular Dichroism (CD) Lipases Produce Optically Active Diglycerides from Achiral Triglycerides , Biochem. Biophys. Res. Commun. 1990, 168, 506-511. 

Lipases (EC 3.1.1.3) are ubiquitous enzymes belonging to the esterase class of hydrolases (see earlier section) and are found in most hving organisms. In nature, lipases catalyze the hydrolytic cleavage of triglycerides into fatty acids and glycerol, or into fatty acid and mono- or diglyceride, at a water-oil interface (Scheme 6.4). 

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... 

The natural substrates of lipases are triglycerides and, in an aqueous environment, lipases catalyze their hydrolysis into fatty acids and glycerol. In anhydrous media, lipases can be active in the reverse reaction [19]. In fact, in the acylation step, acids, lactones, (cyclic) carbonates [20, 21], cyclic amides [22, 23], (cyclic) thioesters [24, 25], and cyclic phosphates [26] have been found to act as suitable acyl donors. In the deacylation step, apart from water, lipases also accept alcohols [27], amines [28, 29], and thiols [30] as nucleophiles although the specificity of lipases is lower for amines and thiols than for water and alcohols [31]. 

Commercial kits are based on the lipase-catalyzed total hydrolysis of the triglyceride, followed by glycerol kinase-catalyzed synthesis of 1-glyceryl phosphate (67) and GPO-catalyzed oxidation of the latter, as shown in equation 17. The end analysis is by a chromogenic oxidation process catalyzed by peroxidase, similar to equation 27, involving 4-aminoantipyrine (81) and 3,5-dichloro-2-hydroxybenzenesulfonate (88)289 or (V-ethyl-(V-(3-sulfopropyl)-m-anisidine (94)289,290. 

LCAT), which catalyzes the synthesis of cholesterol esters (F14, S46, S59) apoA-II, which activates hepatic triglyceride lipase (J2) and apoC-II, which activates lipoprotein lipase, responsible for the hydrolysis of triglycerides in chylomicrons and VLDL (H20, L5). Their mode of action is considered in Section 4 when the individual apolipoproteins are discussed. 

Lipoprotein lipase, an extracellular enzyme, causes the hydrolysis of VLDL and chylomicron triglycerides. Hormone-sensitive lipase catalyzes the hydrolysis of intracellular (storage) triglyceride. 

Kalo, P., Vaara, K., Antila, M. 1986b. Changes in triglyceride position and melting properties of butter fat fraction/rapeseed oil mixtures induced by lipase catalyzed inter-esterification. Fette Seifen Anstrichtm. 88, 362-365. 

Soumanou, M.M., Bornscheuer, U.T., Schmid, U., Schmid, R.D. 1999. Crucial role of support and water activity on the lipase-catalyzed synthesis of structure triglycerides. Biocatal. Biotransform. 16, 443 159. 

Enzymatic Processes. The enzyme hydrolysis of triglycerides is catalyzed by lipases ... 

In the interesterification of fats, 1,3-positional specific lipases catalyze reactions in which only the fatty acids in the a-positions of the triglycerides take part, whereas positional nonspecific lipases are able to catalyze reactions in which the fatty acids from both the a- and / -positions take part. In transesterification between two types of fat, the positional non-specific lipase is therefore able to randomize the fatty acids, resulting in the same fatty acid composition in the triglycerides as obtained in the commercially important chemical randomization process. In ester synthesis, positional non-specific lipases catalyze the reaction with both primary and secondary alcohols whereas positional specific lipases are more or less specific for primary alcohols. 

Two different types of enzymatic time-temperature integrators are described. The first, under the tradename of I-point, is based on a lipase-catalyzed hydrolysis reaction (125). The lipase is stored in a nonaqueous environment containing glycerol. The indicator contains two components that are mixed when the indicator is activated. The operating principle is as follows Upon activation, two volumes of reagents are mixed with each other. Lipase is thereby exposed to its substrate, here a triglyceride. At low temperatures there will be almost no hydrolytic reaction. As the temperature increases, hydrolysis accelerates and protons are liberated. A pH indicator is dissolved in the system. The indicator is selected to shift color after a certain amount of acid has been liberated by the enzyme-catalyzed process. Since the catalytic activity is influenced both by temperature and time, this indicator strip is said to be a time-temperature integrator. 

Using a lipase-immobilized membrane, the FET biosensor made it possible to analyze for triglycerides (7,13,26). Lipase catalyzes the hydrolysis of triglyceride into glycerol and oig anic acid. In an assay for tributylin the FET biosensor gives... 

Triglycerides also are now commonly measured with enzyme reagents directly in plasma or serum. Reagents combining all the required enzymes, cofactors, and buffers are available from various manufacturers, and as for cholesterol, such reagents are optimized for use with particular instrument-calibrator systems. Several different enzyme sequences have been used. In all of the methods, the first step is the lipase-catalyzed hydrolysis of triglycerides to glycerol and fatty acids. 

The choice of immobilization matrix material must be made carefully because its polarity, or aquaphilicity (water-adsorption capability), and the chemistry of its charged surface groups can affect the observed enantioselectivity and the occurrence of side reactions, particularly hydrolysis and isomerization (e.g., of mono-and diglycerides during lipase-catalyzed synthesis of structured triglycerides). In the situations alluded to above, it may be worthwhile to screen the various immobilization matrices. 

FIG. 8.17 Lipase-catalyzed conversion of insoluble oily (triglyceride) soils. 

Various bacterial, fungal and plant lipases have been described to hydrolyze PET (Table 15.1). Lipases catalyze the hydrolysis of long chain water insoluble triglycerides and, unlike cutinase they are interfacially activated in the presence of a water-lipid interface [63-65]. The active site of lipases is covered with a peptide segment called lid while upon opening the active site becomes accessible to the substrate. Consequently, it as been indicated that PET hydrolysis by lipase can be improved in the presence of detergents [55, 66]. Apart from typical lipases and cutinases, other esterases have been shown to hydrolyze PET. Nevertheless, it is not quite clear yet what constitues a PET-hydrolase. On the one hand a comprehensive comparison of all reported enzymes on typical lipase and cutinase substrates in addition to PET is not available. On the other hand, apart from the active site architecture and specificities on water soluble substrates, the adsorption behavior onto polymers will also play a major role. 

Hydrolases catalyze hydrolysis reactions, that is, the addition of a water molecule to a bond resulting in bond breakage. These reactions are important in the digestive process. For example, lipases catalyze the hydrolysis of the ester bonds in triglycerides ... 

Dietary lipids (triglycerides) are emulsified into tiny fat droplets in the intestine by the action of bile salts. Pancreatic lipase catalyzes the hydrolysis of triglycerides into monoglycerides and fatty acids. These are absorbed by intestinal epithelial cells, reassembled into triglycerides, and combined with protein to form chylomicrons. Chylomicrons are transported to the cells of the body through the bloodstream. Fatty acids are stored as triglycerides (triacylglyc-erols) in fat droplets in the cytoplasm of adipocytes. 

The large fat globule that takes up nearly the entire cytoplasm Lipases catalyze the hydrolysis of the ester bonds of triglycerides. 

As compared to other catalyst types used in the production of biodiesel, enzymes have several advantages. They enable conversion under reaction conditions milder than those required for chemical catalysts. Moreover, in the enzymatic process, both the transesteiification of triglycerides and the esterification of fi e fatty acids occur in one process step. However, lipase-catalyzed transesterifications induce a series of drawbacks. As compared to conventional alkaline catalysis protocols, reaction efficiency tends to be rather poor, and thus enzymatic catalysis generally necessitates significantly longer reaction times and higher enzyme amounts. The primary obstacle to the application of enzymes in industrial processes is their relatively high cost [7]. 

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