Lipase inhibitor, enzyme inhibition

Mecfianism of Action A gastric and pancreatic lipase inhibitor that inhibits absorption of dietary fats by inactivating gastric and pancreatic enzymes. Therapeutic Effect Resulting caloric deficit may positively affect weight control. 

Lipase Inhibitor Orlistat (Xenical, Roche) is prescribed for the treatment of obesity. It inhibits the gastrointestinal lipase enzymes by binding to the lipase through the serine site and inactivates the enzyme. Fat in the form of triglycerides cannot be hydrolyzed by the lipase and converted to free fatty acids and monoglycerides. Thus, there is no uptake of fat molecules into the cell tissue. 

Like pancreatic lipase, this enzyme is clearly dependent on a lipid/water interface for maximal activity, where it also may reach a very high catalytic rale, Abo like pancreatic lipase, it is not inhibited by serine esterase inhibitors like DFP orPMSF. 

Decreases in plasma VLDL primarily result from the ability of these compounds to stimulate the activity of lipoprotein lipase, the enzyme responsible for removing triglycerides from plasma VLDL (Fig. 30.5). Additionally, fibrates can lower VLDL levels through PPARa-mediated stimulation of fatty acid oxidation, inhibition of triglyceride synthesis, and reduced expression of apoC-lll. This latter effect enhances the action of lipoprotein lipase, because apoC-lll normally serves as an inhibitor of this enzyme. Favorable effects on FIDL levels appear to be related to increased transcription of apoA-l and apoA-ll as well as a decreased activity of cholesteryl ester transfer protein. 

We succeeded in showing that recycling of the enzyme was indeed possible in our IL solvent system, though the reaction rate gradually dropped with repetition of the reaction process. Since vinyl acetate was used as acyl donor, acetaldehyde was produced hy the hpase-catalyzed transesterification. It is well known that acetaldehyde acts as an inhibitor of enzymes because it forms a Schiff base with amino residue in the enzyme. However, due to the very volatile nature of acetaldehyde, it easily escapes from the reaction mixture and therefore has no inhibitory action on the lipase. However, this drop in reactivity was assumed to be caused by the inhibitory action of acetaldehyde oligomer which had accumulated in the [bmim][PFg] solvent system. In fact, it was confirmed that the reaction was inhibited by addition of acetaldehyde trimer. =... 

In 1987, scientists at Hoffmann-La Roche described their discovery of hpstatin (5), a secondary metabolite isolated from Strptomyces toxytricini, and demonstrated that it is a potent inhibitor of pancreatic lipase.Simple hydrogenation of 5 formed terahydrolipstatin (1,USAN, orlistat) which possesses comparable biological activity but is more stable than 5. Orlistat (1, Xenical ) works through pancreatic lipase inhibition. Pancreatic lipase is the key enzyme of dietary triglyceride absorption, exerting its activity... 

Chemical Inhibition. A large variety of chemical compounds have been added to milk or purified lipase. The conditions under which the inhibitor is studied are very important. Factors such as pH, temperature, time of addition of the chemical, sequence of addition of reactants, and the presence or absence of substrate are undoubtedly involved. The presence of substrate appears to offer some degree of protection to the enzymes. Consequently, in lipase studies, the surface area of the emulsified substrate is probably also important. 

Inhibition of lipases, both by the substrate or the product, has been observed. In alcoholysis of methyl propanoate with n-propanol catalyzed by Candida antarctica lipase B (CALB), the alcohol was found to inhibit the enzyme resulting in a deadend complex [21]. Phosphate- and phosphonate-conlaining inhibitors are known to inhibit proteases. Studies of the inhibition of CALB have shown inhibition by diethyl p-nitrophenyl phosphate. The inactivation of the enzyme was caused by covalent binding of diethyl p-nitrophenyl phosphate in the active site [22]. 

NADH oxidation, and electron transport (Nriagu 1980). Cadmium is a potent enzyme inhibitor, affecting a variety of plant enzymes such as PEP carboxylase, lipase, invertase (Yu 1997), and others. Extensive reports are available concerning Cd-dependent inhibition of enzymes from animals and humans. Alkaline phosphatase and ATPases of myosin and pulmonary alveolar macrophage cells are examples. 

Since MGL is a serine hydrolase, its sensitivity to many of the available serine hydrolase inhibitors has been explored (Table 3). The results support the hypothesis that MGL can be inhibited by compounds that interact with its reactive serine. On the other hand, the potencies of the inhibitors are quite variable in some cases, this likely reflects differences in assay methodology (i.e., substrate concentration, pH, form of the enzyme). However, in a few cases, the same assay conditions revealed very different inhibitory potencies (e.g., compare the platelet and macrophage membrane studies by Di Marzo et al. 1999). In any event, studies of these compounds are not likely to yield selective inhibitors of MGL. All of these compounds are inhibitors of FAAH (see above) and many are also inhibitors of PLA2, diacylglycerol lipase, and acetylcholine esterase, among other hydrolases. By analogy to the development of the URB series of FAAH inhibitors (Kathuria et al. 2003), it is likely that selective inhibitors of MGL will come from other synthetic avenues. 

The lipase from Serratia marcescens has a high enantioselectivity (E = 135) for the (2R,3S)-(4-methoxyphenyl) glycidic acid methyl ester, which acts as a competitive inhibitor. The formed acid (hydrolyzed (+)-methoxyphenylglycidate) is unstable and decarboxylates to give 4-methoxyphenylacetaldehyde this aldehyde strongly inhibits and deactivates the enzyme. It is removed by transfer to the aqueous phase by formation of a water-soluble adduct with sodium hydrogen sulfite added to the aqueous phase. The bisulfite acts also as a buffer to maintain constant pH during synthesis. 

As shown in Fig. (11a), chitin-chitosan inhibited the pancreatic lipase activity dose-dependently between the concentrations of 6.25 p,g/ml and 200 ig/ml in the assay system, using triolein emulsified with lecithin. For characterization of the mechanism involved in the inhibition of pancreatic lipase by chitin-chitosan, the enzyme activity was assayed at various concentrations of lecithin-emulsified triolein and in the presence of increasing concentrations of chitin-chitosan. A Lineweaver-Burk plot of the data in Fig. (11 b) shows that chitin-chitosan was a competitive inhibitor. The Km and Vmax values of the lipase activity for lecithin-emulsified triolein were 6.06 ag/ml and 8.7 nmol/ml/min, respectively. The K value of chitin-chitosan on the lipase activity in lecithin-emulsified triolein was 17.6 M-g/ml. When triolein was emulsified with... 

MNPHP is a well-known irreversible inhibitor of lipases that is highly specific for reaction with active-site serine residues. Thus, MNPHP was selected as the inhibitor to determine, by titration, the fraction of catalytic sites that are accessible and active. Since we are concerned with CALB activity in organic media, inhibition was studied in heptane. LC-MS was used to determine the release of p-nitrophenol (pNP) which corresponds with accessible active sites. To ensure that adsorption of pNP by resins was taken into consideration, pNP concentration was corrected as follows. A fixed quantity of enzyme-free resin was incubated overnight in acetonitrile with different concentrations of j NP. Standard curves of pNP adsorption by each resin as a function of pNP concentration were constructed from LC-MS measurements. MNPHP-inhibited immobilized enzymes were used for e-caprolactone ring-opening polymerizations in toluene (70 C). No conversion of monomer was observed in 30 minutes. Hence, MNPHP titration resulted in complete inhibition of CALB activity. 

Ebelaetones. Enzyme inhibitors with /3-lactone structure from cultures of Streptomyces aburaviensis. E. A C20H34O4, Mr 338.49, needles, mp. 86 °C, [a] - 221 ° (CHjOH)) and . B C2 H3 04,Mr352.51,needles,nip. 77 °C, Icc]d -203° (CH3OH) inhibit membrane-bound esterases, lipases, and aminopeptidases of animal cells as well as cutinases of fungal cells (antifungal activity). 

The enantioselective inhibition of enzymes by the addition of chiral amines functioning as noncompetitive inhibitors has been reported for lipases [288]. This phenomenon is discussed in Sect. 2.1.3.2. For the selectivity enhancement of dehydrogenase reactions via addition of enzyme inhibitors see Sect. 2.2.3. 

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