Isopropylmaleic acid

Another new alkaloid (50) was also isolated from P. heterophylla. Mild acid hydrolysis of (50) gave a desacetyl compound which showed a prominent peak due to the loss of —CH2C02CH3 in its mass spectrum, thereby indicating that the other carboxyl group is esterified to the base. Vigorous acid hydrolysis of (50) gave 1-hydroxymethylpyrrolizidine of undefined stereochemistry together with a neutral compound which yielded (-)-2-isopropylmalic acid on basic hydrolysis. 

The keto-group is subsequently reduced and water is eliminated. By aldol addition, a-isopropylmalic acid is obtained. This is first dehydrated, followed by another addition of water in this way, )S-isoprop)dmalic acid is formed. Oxidative decarboxylation yields a-ketoisocaproic add, which is finally converted into leucine by reductive amination. 

Isopropylmaleic Acid (Dimethylcitraconie add, Z-methyl-l-butylene-1 2-dicarboxylic add)... 

Strassman, M. and Ceci, L.N. (1963) Enzymic formation of a-isopropylmalic acid, an intermediate in leucine biosynthesis. /. Biol Chem., 238,2445-2452. 

In chimeric isopropylmalate dehydrogenase from an extreme thermophile, Thermus thermophile, and a mesophile. Bacillus subtilis, the stability of each chimeric enzyme was also proportional to the content of the amino acid sequence from the T. thermophile enzyme (26). The thermal stability of the chimeras was also intermediate between that of the highly labile Type II hexokinase and the relatively stable Type I isozyme (57). 

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... 

As expected, among the mutants excreting leucine there was a mutant constitutively derepressed with respect to the formation of the enzyme a-isopropylmalate synthetase, which is the first enzyme in the leucine biosynthetic pathway. In another mutant, this enzyme is insensitive to endproduct inhibition by leucine. However, contrary to our expectations, we found mutants carrying regulatory defects in the control of the valine-isoleucine biosynthetic pathway several mutants are constitutively derepressed with respect to the formation of aceto-hydroxy acid synthase and in one mutant this enzyme is insensitive to endproduct inhibition by valine. The selection and the existence of... 

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.

Emptage, M. H. Yeast isopropylmalate isomerase as an iron sulfur protein. In Biosynthesis of Branched Chain Amino Acids, Proc. Workshop Barak, Z. E., Chipman, D. M. and Schloss, J. V., Ed. VCH, 1988, pp 315-328. 

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... 

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.

Figure 1. Reaction intermediate analogue inhibitors of ketol acid reductoiscnnerase (top) and isopropylmalate dehydrogenase (bottom).

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