Carboxylester hydrolase

IUPAC classification of the enzyme has been cither EC.3.1.1.1 (carboxylester hydrolase) or EC. 3. LI.13 (cholesterolester hydrolase) (TbWe 2). 

As increasing research has been carried out with these enzymes, a less empirical approach has been taken as a result of the different substrate profiles that have been compiled for various enzymes in this class. These profiles have been used to construct active site models for such versatile enzymes as the carboxylester hydrolase, pig liver esterase (PLE) (E.C. 3.1.1.1), and the microbial lipases (E.C. 3.1.1.3) from Burkholderia cepacia (formerly Pseudomonas cepacia) lipase (PCL), Candida... 

It is seems clear that further chemical, biochemical and physiological studies of lipase inhibitors will improve our knowledge of this important and interesting family of carboxylester hydrolases. Orlistat was the first lipase inhibitor to be launched on the market. It is to be expected that other molecules will be developed as beneficial drugs for human health. 

Enhanced detoxication Monooxygenase Arylester hydrolase Carboxylester hydrolase Catalytic hydrolysis Insecticide sequestering Glutathione S-transferase y-Aminobutyric acid (GABA) receptor... 

Figure 1. Bioactivation and detoxication of methyl parathion. AH is arylester hydrolase, CH is carboxylester hydrolase, G is glutathione transferase, and M is monooxygenase.

Hydrolases. Hydrolytic mechanisms are also important in insecticide resistance, despite the apparent low activities in resistant insects when compared to mammalian enzymes (Table III). Some strains of resistant mosquitoes (22), Tribolium beetles (24), and Indianmeal moth (22) have specific resistance for malathion and similar carboxylester insecticides. This is due to increased catalytic hydrolysis, possibly through production of a more efficient enzyme (25.26). Californian tobacco budworms with low level permethrin resistance exhibited twice the normal activity of trans-permethrin carboxylester hydrolase (27). 

It is clear that the insecticide of interest must be used to assay for this type of resistance since 1-naphthyl acetate, a general substrate used to stain for many hydrolases, did not detect malathion carboxylester hydrolase (assayed as the hydrolysis of [14C]-malathion) in starch gel electrophoresis of Culex tarsalis (23). Similarly, trans-permethrin hydrolyzing activity of soybean looper was resolved from 1-naphthyl acetate hydrolyzing activity by polyacrylamide gel electrophoresis (28). Malathion carboxylester hydrolases were not correlated with activity toward 1-naphthyl acetate in Drosophila, Anopheles, and Indianmeal moth (25.29.30). 

Green peach aphid carboxylester hydrolase 0.256s (24)... 

This enzyme, purified from aphids (24). was very slow in hydrolyzing paraoxon compared to mammalian arylester hydrolases (Table III) however, it was twice as fast in recovery from paraoxon inhibition compared to a porcine carboxylester hydrolase (35) and >300 times faster than monomeric carboxylester hydrolase of rabbit liver (26). No qualitative differences were found in the enzyme, E4, isolated from resistant and susceptible aphids E4 was one of seven electrophoretic forms of hydrolases observed (34). Recovery indicates that resistance is due to both reaction with the insecticide and a very slow turnover, or catalysis. A similar mechanism of was observed with paraoxon in resistant green rice leafhoppers (37). 

Pancreatic carboxylester lipase, secreted by the pancreas as an active enzyme without proteolytic activation, displays broad substrate specificity and has therefore received many names in the literature carboxylesterase, bile salt-stimulated (or activated or dependent) lipase (due to its absolute requirement for bile salts to hydrolyze insoluble substrates), carboxylester lipase or hydrolase, cholesterol esterase, lysophospholipase, nonspecific lipase, and monoglyceride lipase. The IUPAC classification of the enzyme has been either EC.3.1.1.1 (carboxylester hydrolase) or EC.3.1.1.13 (cholesterolester hydrolase) (Table 2). 

These enzymes occur in various concentrations in all cereals. Carboxylester hydrolase, readily isolated from wheat germ, is not considered a lipase... 

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