Enzyme 3-isopropylmalate dehydrogenase

K Imada, M Sato, N Tanaka, YKatsube, Y Matsuura, T Oshima. Three-dimensional structure of a highly thermostable enzyme, 3-isopropylmalate dehydrogenase of Thermus thermophilus at 2.2 A resolution. J Mol Biol 222 725-738, 1991. 

II. IDEAL MODEL SYSTEM FOR ENZYME ENGINEERING ISOCITRATE AND ISOPROPYLMALATE DEHYDROGENASES... 

Isocitrate dehydrogenase (E.C. 1.1.1.42, IDH) from Escherichia coli and isopropylmalate dehydrogenase (E.C. 1.1.1.85, IMDH) from Thermus thermophilus are involved in Krebs cycle and leucine biosynthesis respectively. Both enzymes catalyze the sequential reactions... 

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). 

It may well be, in some cases. Surface loops are often drastically shortened in hyperthermophilic enzymes examples include T. thermophilus isopropylmalate dehydrogenase," T. maritima ferredoxin, and T. aquaticus glyceraldehyde-3-phosphate dehydrogenase. "... 

The t/ireo-Ds-3-isopropylmalate dehydrogenase from T. thermophilus HB8 has also been studied, again from a view to eluddate mechanisms of stabilization. Purified after first cloning into E. coli [137], the enzyme was shown to be dimeric with an optimum pH of 7.2 and a dependence upon metal ions (Mg " or Mn ) for activity. The enzyme was markedly stabilized by high concentrations (2 M) of KCl, but the mechanism for this is unclear. 

Figure 19.2 Keto-add pathways for the production of n-butanol, isobutanol, and related compounds. Enzyme abbreviations Pyk, pyruvate kinase Ppc, phosphoenolpyruvate carboxylase AspC, aspartate aminotransferase ThrA, apartate kinase/homoserine dehydrogenase asd, aspartate semialdehyde dehydrogenase ThrB, homoserine kinase ThrC, threonine synthase LeuA, 2-isopropylmalate synthase LeuCD, 2-isopropylmalate hydrolyase/3-isopropylmalate...

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