Enoyl-CoA Hydratase Crotonase

Enoyl-CoA hydratase. A specific example of the reaction in Eq. 13-6 is the addition of water to fra s-a,P-unsaturated CoA derivatives (Eq. 13-7). It is catalyzed by enoyl-CoA hydratase (crotonase) from mitochondria and is a step in the P oxidation of fatty acids (Fig. 10-4). 

Enoyl CoA hydratase (crotonase) 2 butyryl CoA dehydrogenase 3 Co A-transferase 4 butyraldehyde dehydrogenase 5 butanol dehydrogenase... 

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... 

FIGURE 24.15 The conversion of trans- and m-enoyl CoA derivatives to l- and d-/3-hydroxyacyl CoA, respectively. These reactions are catalyzed by enoyl-CoA hydratases (also called crotonases), enzymes that vary in their acyl-chain length specificity. A recently discovered enzyme converts ram-enoyl-CoA directly to D-/3-hydroxyacyl-CoA. 

DIHYDROXYACETONE PHOSPHATE ACYLTRANSFERASE ENOYL-CoA HYDRATASE (or, CROTONASE)... 

Enoyl CoA hydratase (also called crotonase or 3-hydroxyacyl CoA hydrolyase)... 

Enoyl-CoA hydratase (ECH commonly known as crotonase), that catalyzes the cofactor-independent hydration of conjugated enoyl-CoA esters in yS-oxidation, has been the subject of considerable debate regarding the timing of bond-making reactions and, therefore, the importance of a thioester enolate anion on the reaction coordinate. The active site contains Glu 144 and Glu 164 as the only possible acid-base catalysts. In the nonphysiological dehydration direction, the value of the pKa... 

Hydratases in the Fatty Acid /3-Oxidation Pathway Enoyl-CoA Hydratase and the Crotonase Superfamily... 

Enoyl CoA hydratase, Short-chain >4 Also called crotonase. Activity decreases with increasing chain length. 

Hydration of the a, -trans double bond is catalysed by enoyl-CoA hydratase (EC 4.2.1.17 crotonase). This enzyme will also attack cw-double bonds and A3-enoyl-CoAs. An l-OH fatty acid is produced (4- in the latter case and 3- in -oxidation) from the trans isomers. The enzyme has been reviewed by Stern (1961). 

Conjugate addition reactions occur in biological systems. An enzyme known as enoyl-CoA hydratase (also known as crotonase) facilitates the conjugate addition of water to the C=C unit of an acyl-CoA molecule such as 94 to give the 3-hydroxy thioester 95. The fragment CoA is coenzyme A, 97, which forms a thioester unit as seen in 94 and 95. This process is essential for the metabolism of fatty acids and the production of energy in which enoyl-CoA hydratase catalyzes the second step in the breakdown of fatty acids or the second step of P-oxidation in fatty acid metabolism. 

Fig. 8. P-Oxidation of fatty acids in E. coli. Long-chain fatty acids are transported into the cell by FadL and converted to their CoA thioesters by FadD (not shown). The acyl-CoAs are substrates for the (1) acyl-CoA dehydrogenase (YafH) to form a trans-2-enoyl-CoA. The double bond is reduced by (2) rrans-2-enoyl-hydratase (crotonase) activity of FadB. The P-hydroxyacyl-CoA is then a substrate for the NADP -dependent dehydrogenase activity of FadB (3). A thiolase, FadA (4), releases acetyl-CoA from the P-ketoacyl-CoA to form an acyl-CoA for subsequent cycles. (5) Polyunsaturated fatty acyl-CoAs are reduced by the 2,4-dienoyl-CoA reductase (FadH). (6) FadB also catalyzes the isomerization of c/s-unsaturated fatty acids to trans. (7) The epimerase activity of FadB converts O-P-hydroxy thioesters to their L-enantiomers via the /rans-2-enoyl-CoA.

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