Lipase, function

Lipase is an enzyme which catalyzes the hydrolysis of fatty acid esters normally in an aqueous environment in living systems. However, hpases are sometimes stable in organic solvents and can be used as catalyst for esterifications and transesterifications. By utihzing such catalytic specificities of lipase, functional aliphatic polyesters have been synthesized by various polymerization modes. Typical reaction types of hpase-catalyzed polymerization leading to polyesters are summarized in Scheme 1. Lipase-catalyzed polymerizations also produced polycarbonates and polyphosphates. 

Hernell, O., Blackberg, L. 1994. Human milk bile salt-stimulated lipase functional and molecular aspects. J. Pediatr. 125 (Suppl. 2), S56-S61. 

Fig. 8.9 Current working model of endothelial lipase function. EL is synthesized by endothelial cells in variety of various tissues, is secreted and binds to HSPGs on the cell surface. There it binds to circulating lipoproteins, hydrolyzing phospholipids and resulting in lipoprotein particles that are reduced in phos-...

W.-J. Shen, S. Patel, and F. B. Kraemer, Hormone-sensitive lipase functions as an oligomer. Biochemistry, 2000, 39, 2392-2398. 

The characteristic features of enzymes in media of low water content are ideally suited for lipases, whose natural substrates usually are of very low water solubility. Consequently, lipase function in nonpolar media and the use of lipase to catalyze various types of reactions such as ester synthesis, transesterification, and ester hydrolysis have been extensively investigated. 

A hydrophilic substrate, acetylsalicylic acid, was subjected to lipase catalyzed hydrolysis in a W/O microemulsion [77]. For comparison, the reaction was also carried out in aqueous buffer. Since hydrolysis of acetylsalicylic acid proceeds spontaneously without added catalyst (intramolecular catalysis), reactions without lipase were performed as controls. It was found that addition of lipase did not affect the rate of reaction in aqueous buffer. However, the reaction in miroemulsion was catalyzed by the lipase, and the rate was linearly dependent on lipase concentration. This is a further illustration of the fact that microemulsions, with their large oil/water interfaces, are suitable media for lipase-catalyzed reactions. The same reactions were also performed using a-chymotrypsin as catalyst. This enzyme, which also catalyzes ester hydrolysis but which, unlike lipase, functions independently of a hydrophobic surface, was not more active in microemulsion than in the buffer solution. 

In another study, lipase functionalized guar gum nanoparticles in the size range 19-32 nm were prepared by nanoprecipitation and crosslinking method for drug delivery applications. It was found that the formation of nanoparticles depends upon the molecular mass of the galactomannan, solvent, surfactant, crosslinker and agitation. In this work, the efficacy of the drug release on the GG nanocarrier was demonstrated... 

Further studies of Pseudomonas sp. lipase revealed a strong influence of the water content of the reaction medium (Entry 20) [48]. To be able to compare the enzyme activity and selectivity as a function of the water present in solvents of different polarities, it is necessary to use the water activity (a ) in these solvents. We used the... 

Esterases have a catalytic function and mechanism similar to those of lipases, but some structural aspects and the nature of substrates differ [4]. One can expect that the lessons learned from the directed evolution of lipases also apply to esterases. However, few efforts have been made in the directed evolution of enantioselective esterases, although previous work by Arnold had shown that the activity of esterases as catalysts in the hydrolysis of achiral esters can be enhanced [49]. An example regarding enantioselectivity involves the hydrolytic kinetic resolution of racemic esters catalyzed by Pseudomonasfluorescens esterase (PFE) [50]. Using a mutator strain and by screening very small libraries, low improvement in enantioselectivity was... 

In principle, numerous reports have detailed the possibility to modify an enzyme to carry out a different type of reaction than that of its attributed function, and the possibility to modify the cofactor of the enzyme has been well explored [8,10]. Recently, the possibility to directly observe reactions, normally not catalyzed by an enzyme when choosing a modified substrate, has been reported under the concept of catalytic promiscuity [9], a phenomenon that is believed to be involved in the appearance of new enzyme functions during the course of evolution [23]. A recent example of catalytic promiscuity of possible interest for novel biotransformations concerns the discovery that mutation of the nucleophilic serine residue in the active site of Candida antarctica lipase B produces a mutant (SerlOSAla) capable of efficiently catalyzing the Michael addition of acetyl acetone to methyl vinyl ketone [24]. The oxyanion hole is believed to be complex and activate the carbonyl group of the electrophile, while the histidine nucleophile takes care of generating the acetyl acetonate anion by deprotonation of the carbon (Figure 3.5). 

Goldstein, N. P. Epstein, J. H. and Roe, H. J. Studies of pancreatic function IV. A simplified method for determination of pancreatic lipase using aqueous tributyrin as substrate, with one hundred normal values by this method. J. Lab. Clin. Med. (1948), 33, 1047-1051. 

On the other hand, the macrolides showed unusual enzymatic reactivity. Lipase PF-catalyzed polymerization of the macrolides proceeded much faster than that of 8-CL. The lipase-catalyzed polymerizability of lactones was quantitatively evaluated by Michaelis-Menten kinetics. For all monomers, linearity was observed in the Hanes-Woolf plot, indicating that the polymerization followed Michaehs-Menten kinetics. The V, (iaotone) and K,ax(iaotone)/ m(iaotone) values increased with the ring size of lactone, whereas the A (iactone) values scarcely changed. These data imply that the enzymatic polymerizability increased as a function of the ring size, and the large enzymatic polymerizability is governed mainly by the reachon rate hut not to the binding abilities, i.e., the reaction process of... 

Terminal-functionalized polymers such as macromonomers and telechelics are very important as prepolymer for construction of functional materials. Single-step functionalization of polymer terminal was achieved via lipase catalysis. Alcohols could initiate the ring-opening polymerizahon of lactones by lipase catalyst. The lipase CA-catalyzed polymerizahon of DDL in the presence of 2-hydroxyethyl methacrylate gave the methacryl-type polyester macromonomer, in which 2-hydroxyethyl methacrylate acted as initiator to introduce the methacryloyl group quanhtatively at the polymer terminal ( inihator method ).This methodology was expanded to the synthesis of oo-alkenyl- and alkynyl-type macromonomers by using 5-hexen-l-ol and 5-hexyn-l-ol as initiator, respechvely. 

The enzymatic polymerization of 12-hydroxydodecanoic acid in the presence of 11-methacryloylaminoundecanoic acid conveniently produced the methacrylamide-type polyester macromonomer. Lipases CA and CC were active for the macromonomer synthesis. Enzymatic selective monosubstitution of a hydroxy-functional dendrimer was demonstrated. Lipase CA-catalyzed polymerization of 8-CL in the presence of the first generation dendrimer gave the poly(8-CL)-monosubstituted dendrimer. 

Organic solvent can affect the enzyme specificity [76]. Authors have indicated that transesterification of l,4-butyloxy-2-octylbenzene and butanol in presence of lipases from Pseudomonas can produce two different products when using hydrophilic (acetonitrile) or hydrophobic (toluene) solvents. Zaks and Klibanov [16], demonstrated that subtilisine and a-chymotrypsine specificites can be changed as a function of solvent types. This is true for a limited number of biocatalysts. 

In a first experiment, the esterification of oleic acid with 1-butanol catalysed by a Rhizomucor miehei lipase was investigated (Scheme 4.3). Lipases usually function at the water/organic interface, which make them extremely suitable for use in the CCS. 

ApoC-I is expressed mainly in liver but also in lung, skin, testis, spleen, neural retina, and RPE. Its multiple functions include the activation of lecithin cholesterol acyltransferase (LCAT) and the inhibition, among others, of lipoprotein and hepatic lipases that hydrolyze triglycerides in particle cores. Notably, both LCAT and lipoprotein lipases are expressed in RPE and choroid (Li et al., 2006). Moreover ApoC-I has been shown to displace ApoE on the VLDL and LDL and thus hinder their binding and uptake via their corresponding receptors (Li et al., 2006). 

ApoC-II is expressed in liver and intestine, and both the neural retina and RPE (Li et al., 2006). In contrast to ApoC-I, it can function as an activator of lipoprotein lipase. Similar to ApoA-I, ApoA-II, and ApoE, in the absence of lipid to stabilize its structure, ApoC-II forms amyloid assemblies. 

A combination of an enzymatic kinetic resolution and an intramolecular Diels-Alder has recently been described by Kita and coworkers [23]. In the first step of this domino process, the racemic alcohols ( )-8-55 are esterified in the presence of a Candida antarctica lipase (CALB) by using the functionalized alkenyl ester 8-56 to give (R)-8-57, which in the subsequent Diels-Alder reaction led to 8-58 in high enantioselectivity of 95 and 91 % ee, respectively and 81 % yield (Scheme 8.15). In-... 

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