Palmitoyl-CoA hydrolase

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 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. 

M. Robbi, H. Beaufay, Cloning and Sequencing of Liver Carboxylesterase ES3 (Egasyn) , Biochem. Biophys. Res. Commun. 1994, 203, 1404-1411 M. Robbi, E. Van Schaftingen, H. Beaufay, Cloning and Sequencing of Rat Liver Carboxylesterase ES-4 (Microsomal Palmitoyl CoA Hydrolase) , Biochem. J. 1996, 313(Part 3), 821-826. 

R. Mentlein, H. Rix-Matzen, E. Heymann, Subcellular Localization of Nonspecific Carboxylesterases, Acylcarnitine Hydrolase, Monoacylglycerol Lipase and Palmitoyl-CoA Hydrolase in Rat Liver , Biochim. Biophys. Acta 1988, 964, 319-328. 

Berge, R.K., Skrede, S. Farstad, M. (1981) Febs Lett. 124, 43-47. Effects of clofibrate on the intracellular localization of palmitoyl-CoA hydrolase and palmitoyl-L-camitine hydrolase in rat liver. 

Figure 11.5 Reactions of the fatty acid synthase complex. A single multi-subunit enzyme is responsible for the conversion of acetyl-CoA to palmitate. The subunits in the enzyme are (i) acetyltransferase, (ii) malonyltransferase, (iii) oxoacyl synthase, (iv) oxoacyl reductase, (v) hydroxyacyl dehydratase, (vi) enoyl reductase. Finally, a separate enzyme, thioester hydrolase, hydrolyses palmitoyl-CoA to produce palmitate (vii).

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