Enoyl hydratase

A closely related E. coli protein is a 79-kDa multifunctional enzyme that catalyzes four different reactions of fatty acid oxidation (Chapter 17). The amino-terminal region contains the enoyl hydratase activity.32 A quite different enzyme catalyzes dehydration of thioesters of (3-hydroxyacids such as 3-hydroxydecanoyl-acyl carrier protein (see Eq. 21-2) to both form and isomerize enoyl-ACP derivatives during synthesis of unsaturated fatty acids by E. coli. Again, a glutamate side chain is the catalytic base but an imidazole group of histidine has also been implicated.33 This enzyme is inhibited irreversibly by the N-acetylcysteamine thioester of 3-decynoic acids (Eq. 13-8). This was one of the first enzyme-activated inhibitors to be studied.34... 

Creutzfeldt-Jakob disease 248 Crick, Francis H. C. 84, 200 Cristae of mitochondria 14 Crossing-over 18 Crosslinking 79 Crotonase. See Enoyl hydratase Crowfoot Hodgkin, Dorothy M. 84 Cruciform structure in nucleic acids 229 Crustacea 24 Cruzain 619 Cryoenzymology 469 elastase 616 Cryoprotectants 191 Crystallins 169 Crystallography 131-137 electron 131 X-ray 132-137 Crystals, liquid 392-394 Crystal systems 133 Cubic symmetry... 

Enoyl-acyl carrier protein reductase 777 Enoyl hydratase 681 Enoyl reductase 766... 

And it s in that same position we get aqueous addition That is catalysed by enoyl hydratase OH addition s onto carbon number 3 (Creating thus a centre of as5mimetry)... 

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.

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

IV. Addition and elimination involving carbon-carbon (enolate anions) a. Dehydration of alcohols—enoyl hydratase, fumarase, aconitase... 

Another enzyme that bears a close resemblance to bifunctional acid-base catalysts is enoyl-CoA hydratase (ECH). This enzyme is discussed here as an example of an enolate-stabilizing enzyme. The mechanism of ECH involves an enolate intermediate that is formed upon addition of a nucleophile, water molecule, to an a,p-unsaturated thioester. This reaction is the second step in the metabolic oxidation of fatty acids. The X-ray structures of enoyl hydratase enzymes complexed with various substrates analogs are available [29, 30]. A simplified view of the mechanism of ECH is presented in Scheme 6.14. The lifetime of the enolate intermediate is not... 

A summary of the sequential reactions of the -oxidation cycle and the relationship of the overall process to energy metabolism in mitochondria is shown in Figure 3.20. Two carbon units (as acetyl-CoA) are removed from the fatty acyl-Co A substrate by the successive action of four enzymes - acyl-CoA dehydrogenase, enoyl hydratase, a second dehydrogenase and a thiolase. These enzymes are detailed in Table 3.12. 

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