Hydrolase thiolester

Second, esterases have broad (or even very broad) and overlapping substrate specificities. For example, carboxylesterase (EC 3.1.1.1) also catalyzes reactions characteristic of a number of other hydrolases. The discovery that individual isoenzymes of carboxylesterases may be identical to or closely related to acylglycerol lipase, acylcamitine hydrolase, and palmitoyl-CoA hydrolase (see Sect. 2.4.3) has increased the confusion surrounding esterase classification [59], Many esterases are able to hydrolyze amides, thiolesters,... 

Thiolester hydrolases (EC 3.1.2) play an important role in the biochemistry of lipids. They catalyze the hydrolysis of acyl-coenzyme A thiolesters of various chain lengths to free fatty acids and coenzyme A. The current list of over 20 specific enzymes includes acetyl-CoA hydrolase (EC 3.1.2.1), pal-mi toy 1-Co A hydrolase (EC 3.1.2.2), and an acyl-CoA hydrolase (EC 3.1.2.20) of broad specificity for medium- to long-chain acyl-CoA [128],... 

Thiolester hydrolases are present in most tissues and cell compartments. High concentrations are found in liver microsomes and in brown adipose tissue mitochondria and peroxisomes. Several acyl-CoA hydrolases have shown a close relationship to the nonspecific carboxylesterases EC 3.1.1.1. Thus, palmitoyl-CoA hydrolase purified from rat liver microsomes was found to be identical to esterase pI 6.2I6A (ES4 type). An acyl-CoA hydrolase was isolated that showed high similarity to esterase pI 6.1 [74a] [129] [130]. These few examples are further illustrations of the unsatisfying situation of the traditional classification of esterases. 

Thioesters play a paramount biochemical role in the metabolism of fatty acids and lipids. Indeed, fatty acyl-coenzyme A thioesters are pivotal in fatty acid anabolism and catabolism, in protein acylation, and in the synthesis of triacylglycerols, phospholipids and cholesterol esters [145], It is in these reactions that the peculiar reactivity of thioesters is of such significance. Many hydrolases, and mainly mitochondrial thiolester hydrolases (EC 3.1.2), are able to cleave thioesters. In addition, cholinesterases and carboxylesterases show some activity, but this is not a constant property of these enzymes since, for example, carboxylesterases from human monocytes were found to be inactive toward some endogenous thioesters [35] [146], In contrast, allococaine benzoyl thioester was found to be a good substrate of pig liver esterase, human and mouse butyrylcholinesterase, and mouse acetylcholinesterase [147],... 

Larsson, R. Ramstrom, O. Dynamic combinatorial thiolester libraries for efficient catalytic self-screening of hydrolase substrates. Ear. J. Org. Chem. 

The dynamic features of the transthiolesterification reaction have been probed for a range of components of different character, resulting in potent thiolester libraries. The libraries were also exposed to selection by a variety of different hydrolases, where performance and selectivity of the dynamic... 

Scheme 23.4 Production of methylketones from fatty acids by Penicillium roqueforti. 1 ATP-de-pendent acylcoenzyme A (acyl-CoA) synthase 2 flavin adenine dinucleotidedependent acyl-CoA dehydrogenase 3 enoyl-CoA hydratase 4 NAD-dependent 3-hydroxyacyl-CoA dehydrogenase 5 3-oxoacyl-CoA thiolase 6 3-oxoacyl-CoA thiolester hydrolase and 3-oxoacid decarboxylase. (Adapted from [46])...

Hydrolase enzymes were initially chosen as target proteins to catalyze and amplify the optimal constituents from dynamic systems. Among the six enzyme classes, hydrolases (EC 3) are one of the most commonly used, both in bulk industrial processes as well as for laboratory scale reactions [1]. These enzymes do not require any cofactors to perform the reactions, and a large variety is commercially available. Hydrolases furthermore catalyze reactions for a broad range of substrates, e.g., hydrolysis of esters, amides, thiolesters, etc., often accompanied with high stereoselectivity. An example of hydrolases is the family of serine hydrolases, which employs... 

An early example of DSR employed dynamic thiolester systems, generated from transthiolesterification reactions, combined with hydrolases in aqueous solution [2, 3]. The transthiolesterification reaction, of fundamental biological importance [4], is the reversible reaction between a thiolester and a thiol. This dynamic reaction is rapid and sufficiently stable under mild conditions in aqueous solution. Dynamic thiolester systems could thus efficiently be generated from a series of thiolester compounds and thiols. During equilibration, the hydrolase was applied as an external selection pressure to resolve the fittest constituents of the system, where the optimal thiolesters were continuously hydrolyzed to acid and thiol products. During... 

The acyl-CoA conjugates thus formed are seldom excreted, but they can be isolated and characterized relatively easily in in vitro studies. They may also be hydrolyzed back to the parent acid by thiolester hydrolases (EC... 

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