Isopropylmalate dehydratase

ISOPROPYLMALATE DEHYDRATASE 3-ISOPROPYLMALATE DEHYDROGENASE 2-ISOPROPYLMALATE SYNTHASE ISOPULLULANASE ISOSBESTIC POINT... 

Biosynthesis Leu is formed from pyruvic acid - 2-acetolactic acid [acetolactate synthase (EC 4.1.3.18.)+(l-hydroxyethyl)-TPP] - 2,3-dihydroxy-isovaleric acid [reductase+NAD(P)H] - 2-oxoisova-leric acid [dihydroxyacid dehydratase] - 2-isopropyl-malate [2-isopropylmalate synthase + acetyl-CoA (EC 4.1.3.12)] -> 3-isopropylmalate [isopropylmalate dehydratase (EC 4.2.1.33) -HjO+HiO] 2-oxo-isocaproate [3-isopropylmalate dehydrogenase (EC 1.1.1.85) + NAD ] L. [leucine aminotransferase (EC... 

The 3-methyl-2-oxobutanoate, which undergoes tranamination from alanine (Ala, A) to lead to valine (Val, V), also serves as a point from which the biosynthesis of leucine (Leu, L) can begin to be discussed. Thus, as shown in Scheme 12.18, 3-methyl-2-oxobutanoate reacts with acetyl-CoA (CH3COSC0A) in the presence of 2-isopropylmalate synthase (EC 2.3.3.13) to generate (2S)-2-isopropylmalate, which then loses water (isopropylmalate dehydratase, EC 4.2.1.33) to generate 2-isopropylmaleate. Now, water readds under the influence of the same enzyme to... 

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... 

Ahpiperidine-2,6-dicarboxylate dehydrogenase (Q) N-succinyl-2-amino-6-ketopimelate synthase succinyl diaminopimelate aminotransferase succinyl diaminopimelate desuccinylase diaminopimelate epimerase diaminopimelate decarboxylase (Q threonine dehydratase (serine dehydratase) acetolactate synthase acetohydroxy acid isomeroreductase dihydroxy acid dehydratase valine aminotransferase a-isopropylmalate synthase isopropylmalate isomerase -isopropylmalate dehydrogenase leucine aminotransferase... 

Figure 7 Other dehydratases that may use a [4Fe-4S] cluster in an analogous manner to aconitase. A. Isopropylmalate isomerase. B. Fumarase. C. Dihydroxyacid dehydratase. D. Maleic acid hydratase.

Regulation of the synthesis of the branched-chain amino acids, like that of the aspartate family, can be viewed in a temporal framework (Fig. 8). However, the nature of the controls associated with the pathway enzymes do not necessarily suggest an obligatory sequence of regulatory interactions. The sequence illustrated in Fig. 8 assumes that each of the end-products would initially be synthesized from its respective precursors. As isoleucine biosynthesis is reduced by inhibition of threonine dehydratase, the competition between pyruvate and 2-oxobutyrate for the active site of acetohydroxyacid synthase would be diminished. This could result in an increased rate of synthesis of leucine and valine (Fig. 8, 2). Leucine would eventually inhibit isopropylmalate synthase and, to a lesser extent, acetohydroxyacid synthase (Fig. 8, 3). The reduced flow of carbon through the pathway would be utilized for the synthesis of valine. As the concentration of valine increased, the activity of acetohydroxyacid synthase would be sharply curtailed due to... 

Figure 15.4 Isobutanol and 2-methyl butanol (2MB) production via keto acid pathway in cyanobacteria. Gene/protein symbols are dmA, citramalate synthase leuCD, isopropylmalate isomerase leuB, 3-isopropylmalate dehydrogenase AHAS, acetohydroxyacid synthase ilvC, acetohydroxy acid isomeroreductase ilvD, dihydroxy acid dehydratase kivd, ketoisovalerate decarboxylase yqhD, alcohol dehydrogenase.

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