Long-chain enoyl-CoA hydratase

Despite the fact that numerous enzymes have been characterized that catalyze the addition of water to unsaturated fatty acids that are coupled to CoA or ACP, such as methylglucatonyl-CoA hydratase (E.C. 4.2.1.18), lactoyl-CoA dehydratase (E.C. 4.2.1.54), 3-hydroxybutyryl-CoA dehydratase (E.C. 4.2.1.55), itaconyl-CoA dehydratase (E. C. 4.2.1.56), isohexenylglutaconyl-CoA hydratase (E. C. 4.2.1.57), farnesyl-CoA dehydratase (E.C. 4.2.1.57), long-chain enoyl-CoA hydratase (E.C. 4.2.1.74), 3-hydroxydecanoyl-ACP dehydratase (E.C. 4.2.1.60) and 3-hydroxypalmitoyl-ACP dehydratase (E.C. 4.2.1.61), these enzymes are seldomly applied in organic synthesis. 

The second step of the P-oxidation spiral is the reversible hydration of 2-trans-enoyl-CoA to yield L-3-hydroxyacyl-CoA, catalyzed by enoyl-CoA hydratase. However, in fungi 2-tra 5-enoyl-CoA is hydrated by peroxisomal D-3-hydroxyacyl-CoA dehydratase to form D-3-hydroxyacyl-CoA. Enoyl-CoA hydratases are usually associated with the N-terminal region of multifunctional proteins except for the mitochondrial matrix enoyl-CoA hydratase and the E. coli long-chain enoyl-CoA hydratase (see Table 1). D-3-hydioxyacyl-CoA dehydratases are located on the C-terminal domain of the peroxisomal D-specific bifunctional P-oxidation enzyme or the central domain of 1 P-hydroxysteroid dehydrogenase type IV. ... 

Yang, S.-Y. (1994) Comp. Biochem. Physiol. 109B, 557-566. The large subunit of the pig heart mitochondrial membrane-bound P-oxidation complex is a long-chain enoyl-CoA hydratase 3-hydroxyacyl-CoA dehydrogenase bifunctional enzyme. 

W4 C29F3.1 TACGTG- —567 long-chain enoyl-CoA hydratase... 

Two enzymes have been identified in heart mitochondria one is crotonase or short-chain enoyl-CoA hydratase, the second is a long-chain enoyl-CoA hydratase. Crotonase activity is so high in some tissues that the second enzyme may have little function in j -oxidation there (e.g. in liver). However, in most tissues they probably co-operate In fatty acid degradation... 

Enzymes 7,9, and 13 form a trifunctional protein associated with the inner face of the inner mitochondrial membrane. Very-long-chain acyl-CoA dehydrogenase is also associated with other inner mitochondrial membranes while the other enzymes are in the matrix and may be loosely associated with the inner face of the inner membrane. A medium-chain 2-enoyl-CoA hydratase may also be present in the mitochondrial matrix. 

Mitochondria contain three acyl CoA dehydrogenases which act on short-, medium- and long-chain acyl CoAs, respectively. In contrast, there is just one each of the enzymes enoyl CoA hydratase, hydroxyacyl CoA dehydrogenase and (3-ketothiolase which all have a broad specificity with respect to the length of the acyl chain. 

Yeasts are able to degrade long-chain alkanes. The initial hydroxylation is carried out in micrososmes by cytochrome P-450, while degradation of the alkanoate is carried out in peroxisomes that contain the P-oxidation enzymes alkanoate oxidase, enoyl-CoA hydratase, and 3-hydroxyacyl-CoA dehydrogenase. Further details are given in Chapter 4, Sections 4.4.1.2 and 4.4.4. 

Fig. 2. Model of the functional and physical organization of P-oxidation enzymes in mitochondria. (A) P-Oxidation system active with long-chain (LC) acyl-CoAs (B) P-oxidation system active with medium-chain (MC) and short-chain (SC) acyl-CoAs. Abbreviations T, camitineiacylcamitine translocase CPT 11, carnitine palmitoyltransferase 11 AD, acyl-CoA dehydrogenase EH, enoyl-CoA hydratase HD, t-3-hydroxyacyl-CoA dehydrogenase KT, 3-ketoacyl-CoA thiolase VLC, very-long-chain.

Trifunctional Protein 12-16 Complex of long-chain enoyl hydratase, acyl CoA dehydrogenase and a thiolase with broad specificity. Most active with longer chains. 

Figure 1. Comparison of the amino acid sequence in the N-terminal domain of the . coli multifunctional protein (MP) with those of homologous regions of rat peroxisomal trifunctional enzyme (TE), plant gly-oxysomal tetrafunctional protein (PT), pig mitochondrial long-chain-specific bifunctional enzyme (LT)," and rat mitochondrial enoyl-CoA hydratase (EH). Gly" , Glu , and Glu of MP, which are conserved in all known enoyl-CoA hydratases, are indicated by asterisks.

He, X.-Y., Yang, S.-Y. Schulz, H. (1992) Arch. Biochem. Biophys. 298, 527-531. Inhibition of enoyl-CoA hydratase by long-chain L-3-hydroxyacyl-CoA and its possible effect on fatty acid oxidation. 

Engel, C.K., Kiema, T.R., Hiltunen, J.K. Wierenga, R.K. (1998) J. Mol Biol 275, 847-859. The crystal stmcture of enoyl-CoA hydratase complexed with octanoyl-CoA reveals the structural adaptations required for binding of a long chain fatty acid-CoA molecule. 

Inhibition of the 3-ketoacyl-CoA thiolase step (with the likely accumulation of 3-ketoacyl-CoA esters) or the 3-hydroxyacyl-CoA dehydrogenase, with accumulation of 3-hydroxyacyl-CoA esters, could lead to feedback inhibition of Poxidation (see Fig. 1). The 3-hydroxyacyl-CoA dehydrogenases, enoyl-CoA hydratases and short-medium-and long- chain acyl-CoA dehydrogenases can be all be inhibited by 3-ketoacyl-CoA esters. The enoyl-CoA hydratases catalyse an equilibrium but can be inhibited by their 3-hydroxyacyl-CoA products. Finally, the acyl-CoA dehydrogenases are subject to inhibition by their 2-enoyl-CoA products and, hence, feedback inhibition has been viewed as potentially very important in the regulation and control of P-oxidation flux. 

Biochemical studies in fibroblasts from the index patient showed that the rate of P-oxidation of myristate and palmitate was severely decreased to less than 5% of the controls (Table 1). Enzyme measurements of the very-long chain acyl-CoA dehydrogenase, enoyl-CoA hydratase, 3-hydroxyacyl-CoA dehydrogenase, thiolase, carnitine palmitoyltransferase I and II showed normal activities (not shown). The severe deficiency of long chain fatty acid oxidation was explained by the complete deficiency of CAC activity (Table 1). 

Lazarow and de Duve (1976) purified peroxisomes from rat liver and found that these were able to oxidize long chain acyl-CoA esters apparently via a (3-oxidation mechanism (Lazarow, 1978). This peroxisomal system differs distinctly from the well-characterized (3-oxidation system of mitochondria in a number of ways. The first dehydrogenation is carried out by an EAD dependent fatty acyl-CoA oxidase (Lazarow, 1978 Osumi and Hashimoto, 1978) and involves the reduction of O2 to H2O2. The enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase activities are carried out by a multifunctional protein (Osumi and Hashimoto, 1979, 1980). Also, the peroxisomal (3-ketothiolase has different chromatographic properties and chain length specificity from the mitochondrial enzyme (Krahling and Tolbert, 1981). 

Following the eatalytic reaction to form long-chain fatty acyl-CoA, the enzymatic reaction of carnitine palmitoyltranferase I (CPT-1) replaces CoA with carnitine to form fatty acylcamitine [62]. This conversion allows fatty acids to be transported from the cytoplasm to the inner mitochondrial membrane via carnitine acylcamitine translocase. Once across the inner mitochondria membrane, fatty acylcamitine is reversely converted back to long-chain fatty acyl-CoA by carnitine palmitoyltrandferase II (CPT-2) for subsequent P-oxidation [63, 64]. Each p-oxidation cycle removes a two carbon unit and involves four main enzymes 1) aeyl-CoA dehydrogenase, 2) enoyl-CoA hydratase, 3) 3-hydroxyacyl-CoA dehydrogenase, and 4) P-ketothiolase [65]. The net reaction of each P-oxidation pathway is ... 

Acylcarnitines cross the inner mitochondrial membrane (I.M.M.) via a carrier, after which the acyl-CoA is reformed by CPT2, again membrane-bound. The first few rounds of -oxidation are catalyzed by VLCAD and MTP (containing TCHAD, enoyl-CoA hydratase and long-chain oxothiolase... 

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