A-Acetolactic decarboxylase

INSULIN AND OTFiER ANTIDIABETIC AGENTS] (Vol 14) a-Acetolactate decarboxylase [9025-02-9]... 

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 addition, cofactor engineering has been used to deliberately modify the intracellular NADH/NAD+ ratio that plays a predominant role in controlling the Lactococcus lactis fermentation pattern. The introduction of the nox gene, which codes for a NADH oxidase (NOX) that converts molecular oxygen to water at the expense of NADH, to a strain with an inactivated copy of the aldB gene for a-acetolactate decarboxylase led to the efficient metabolism of the na-... 

The newest enzyme for use in beer is acetolactate decarboxylase, used to decrease the fermentation time, by avoiding the formation of diacetyl. Externally or internally produced a-acetolactate decarboxylase transforms the a-acetolactate to acetoin (acetylmethylcarbinol) without the enzyme, acetolactate goes to diacetyl, and then a secondary fermentation slowly reduces it to acetoin. Avoiding or reducing the secondary fermentation results in significant reduction in storage capacity and money tied up in inventory Q). Normally acetolactate forms by the thiaminepyrophosphate-catalyzed acyloin condensation of acetaldehyde and pyruvic acid (2) or by the condensation of two pyruvic acid molecules to yield acetolactate and CC. Acetolactate is important in the synthesis of isoleucine and valine by the yeast. The acetolactate left at the end of the primary fermentation is oxidized spontaneously in a nonenzymatic reaction to diacetvl and C0.> (Eqn. 1)... 

One way to avoid the off-flavor is to introduce an alternative route of degradation of a-acetolactate directly to acetoin. a-Acetolactate decarboxylases from different organisms were successfully overexpressed in the beer-producer strains, accelerating the brewing process by diminishing the time of lagering by weeks [87]. 

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].

Curie, M., Stuer-Lauridsen, B., Renault, R, Nilsson, D. (1999). A general method for selection of a-acetolactate decarboxylase-deficient Lactococcus lactis mutants to improve diacetyl formation. Applied and Environmental Microbiology, 65, 1202-1206. 

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). 

Goupil-Feuillerat N, Cocaign-Bousquet M, Godon J-J, Ehrlich SD, Renault P (1997) Dual role of a-acetolactate decarboxylase in Lactococcus lactis subsp. lactis. J Bacteriol 179 6285-6293... 

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.

Crout DHG, Littlechild J, Morrey SM. Acetoin metaboUsm stereochemistry of the acetoin produced by the pyruvate decarboxylase of wheat germ and by the a-acetolactate decarboxylase of Klebsiella aerogenes. J. Chem. Soc., Per-kinTrans. 1 1986 105-108. 

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