Acetolactate dehydrogenase

Diacetyl synthase 2 acetoin dehydrogenase 3 d-(—)-butanediol dehydrogenase 4 acetolactate dehydrogenase 5 acetolactate synthase... 

Fig. 3. Generation of propionyl-CoA from the isoleucine biosynthetic pathway. The intermediate 2-ketobutyrate can be decarboxylated by either the 2-oxoacid dehydrogenase complex or at low efficiency by the pyruvate dehydrogenase complex. Inhibition of the threonine deaminase by isoleucine and of the acetolactate synthase by herbicides are indicated with dashed arrows...

Thiamin-dependent enzymes, ACETOLACTATE SYNTHASE BENZOYLFORMATE DECARBOXYLASE BRANCHED-CHAIN a-KETO ACID DEHYDROGENASE COMPLEX... 

Scheme 23.5 Metabolic pathways of lactic acid bacteria leading from pyruvate to a-acetolactate and acetoin and chemical diacetyl formation. ALS a-acetolactate synthase, ALDB a-acetolactate decarboxylase, DDH diacetyl dehydrogenase. (Adapted from [72])...

In brewery processes, the bad taste of diacetyl spoils the beer. By addition of ADC (Novo, Bagsvaerd, Denmark) or by cloning and overexpression of ADC in brewery yeast (Kirin, Japan) acetolactate is first decarboxylated to acetoin and then reduced to innocuous 2,3-dihydroxybutane by yeast alcohol dehydrogenase (YADH). 

PUTATIVE PYRUVATE DECARBOXYLASE C13A11 PYRUVATE DEHYDROGENASE El COMPONENT ACETOLACTATE SYNTHASE. 

TPP involved in reactions catalysed by pyruvate decarboxylase (alcoholic fermentation), pyruvate dehydrogenase a-ketoglutarate dehydrogenase (TCA cycle), transketolase (photosynthesis Calvin cycle) acetolactate synthetase (Val, Leu biosynthesis)... 

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 7.1. Overview of the biochemical routes leading to glycerol, pyruvate, and ethanol. Furthermore, valine biosynthesis and diacetyl formation are shown, which may be bypassed by introduction of a heterologous a-acetolactate decarboxylase that directly converts a-acetolactate to acetoin. GPDl and GPD2, glycerol dehydrogenases 1 and 2 ADHl, alcohol dehydrogenase 1 ILV2, acetolactate synthetase ID/5, acetolactate reductoisomerase [Refs in 502].

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... 

Figure 5.1 Production pathways of selected products discussed in the text. Gene/protein symbols aroF, DAMP synthase pykF, pyruvate kinase IdhA, lactate dehydrogenase alaA, alanine transaminase ilvIH, acetolactate synthase (a/sS = heterologous enzyme...

Fig. 1. Bio thetic pathways for the essential aspartate-family amino adds. The numbers represent enzymes catalyzing the reaction 1, aspartate kinase 2, homoserine dehydrogenase 3, homoserine kinase 4, threonine thase 5, threonine dehydrogenase 6, acetolactate thase 7, dihydrodipicolinate thase 8, diaminopimelate decarboiylase.

The biosynthetic pathway of tetramethylpyrazine requires two pyruvate units, one of which is transferred to the thiamine diphosphate (TPP) cofactor under decarboxylation to give 2-(l-hydroxyethyl)thiamine diphosphate 55. The latter adds an acetyl group to the second pyruvate unit by acetolactate synthase (AS) to give (5)-2-acetolactate 56 (Figure 6.70). Subsequent decarboxylation converts (5)-2-acetolactate 56 to acetoin 57. Oxidation of the latter catalyzed by acetoin dehydrogenase (AD) forms butanedione 59. Transamination of butanedione 59 generates 3-aminobutanone 60. Alternatively, a transamination reaction of acetoin 57 proceeds... 

Figure 13.4 Diacetyl production from citrate. CL, citrate lyase OD, oxaloacetate decarboxylase LDH, lactate dehydrogenase AS, a-acetolactate synthase PDHC, pyruvate dehydrogenase complex.

Figure 13.5 Diacetyl production from pyruvate. The chemical oxidative decarboxylation of a-acetolactate into diacetyl is shown by a dotted arrow. ALS, a-acetolactate synthase PDHC, pymvate dehydrogenase complex DS, diacetyl synthase.

Fig. 10.33. Formation of diacetyl and butanediol from citrate by Streptococci. 1 citratase, 2 oxaloac-etate decarboxylase, 3 pyruvate decarboxylase, 4 a-acetolactate synthase, 5 diacetyl reductase, 6 a-acetolactate decarboxylase, 7 2,3-butanediol dehydrogenase...

Three enzymes are involved in the synthesis of 2,3-BD a-acetolactate synthase (EC 4.1.3.18), a-acetolactate decarboxylase (EC 4.1.1.5), and butanediol dehydrogenase (also known as diacetyl [acetoin] reductase Larsen and Stormer 1973 Johansen et al. 1975 Stormer 1975). Two different enzymes form acetolactate from pyruvate. The first, termed catabolic a-acetolactate synthase, has a pH optimum of 5.8 in acetate and is part of the butanediol pathway. The other enzyme, termed anabolic a-acetolactate synthase or acetohydroxyacid synthetase, has been well studied and characterized and will not be discussed here. This enzyme is part of the biosynthetic pathway for isoleucine, leucine, and valine and is coded for by the ilvBN, ilvGM, and ilvH genes in E. colt and Salmonella typhimurium (Bryn and Stormer 1976). 

Figure 1.2. Citrate metabolism in Lactococcus, Leuconostoc, and Weissella species. Key for the enzymes CL, citrate lyase OAD, oxaloacetate decarboxylase LDH, lactate dehydrogenase PDC, pyruvate decarboxylase ALS, a-acetolactate synthase ADC, a-acetolactate decarboxylase DAR, diacetyl acetoln reductase BDH, 2,3-butanediol dehydrogenase Tppi, thiamine pyrophosphate.

Platteeuw, C., Hugenholtz, J., Starrenburg, M., et al. (1995) Metabolic engineering of Lactococcus lactis influence of the overproduction of alpha-acetolactate synthase in strains deficient in lactate dehydrogenase as a function of culture conditions. AppZ Environ Microbiol 61, 3967—3971. 

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