Lactyl-CoA dehydratase

Perhaps the most unusual of this group is lactyl-CoA dehydratase as isolated... 

Abeles and co-workers extended the work of Buckel on the properties and mechanism of the reductive dehydration of lactate to propionate in C. propionicum (234, 235). Studies by Abeles concluded that acrylate is indeed an intermediate in lactate dehydration, based on the observation of a primary kinetic isotope effect of 1.8 on the conversion of [3- H3]lactate to propionate, indicating that -hydrogen abstraction is at least partially rate limiting. The true substrates for the reaction were determined to be the CoA thioesters of lactate and acrylate, hence the enzyme has been aptly named lactyl-CoA dehydratase (234). The reaction was found to be mediated by two proteins, El and E2, and like the (R)-2-hydroxyglutarate-dehydrating enzyme from A. fermentans, both El and E2 from... 

I, pyruvate kinase 2, OS17 enzyme 3, 3-hydroxypropionyl-CoA dehydratase 4, lactate dehydrogenase 5, CoA transferase 6, 3-hyd roxy propiony l-CoA/3-hyd roxy i sobutryl-CoA hydrolase 7, lactyl-CoA dehydratase 8, pyruvate/glutamate transaminase 9, alanine dehydrogenase 10, alanine 2,3-aminomutase ... 

Other enzymes in the aconitase family include isopropylmalate isomerase and homoaconitase enzymes functioning in the chain elongation pathways to leucine and lysine, both of which are pictured in Fig. 17-18.90 There are also iron-sulfur dehydratases, some of which may function by a mechanism similar to that of aconitase. Among these are the two fumarate hydratases, fumarases A and B, which are formed in place of fumarase C by cells of E. coli growing anaerobically.9192 Also related may be bacterial L-serine and L-threonine dehydratases. These function without the coenzyme pyridoxal phosphate (Chapter 14) but contain iron-sulfur centers.93-95 A lactyl-CoA... 

---