Acetolactate decarboxylase

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

The enzyme, df-acetolactate decarboxylase (ALDC), has been developed and coimnercialized in the beginning of the nineties. ALDC catalyzes the decarboxylation of hf-acetolactate to acetoin during the primary fermentation, thereby redncing the prodnction of diacetyl and, consequently, eliminating or greatly redncing the need for a matnration period. 

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-... 

As a side activity, many decarboxylases catalyze the formation of C-C bonds. In the reaction of two pyruvate molecules, catalyzed by pyruvate decarboxylase (PDC, E.C. 4.1.1.1), a-acetolactate is formed, an important intermediate of valine biosynthesis. In turn, a-acetolactale can be oxidatively decarboxylated by oxygen to diacetyl or enzymatically decarboxylated by acetolactate decarboxylase (ADC, E.C. 4.1.1.5) to (] )-acetoin (Figure 7.29). 

Although the utility of transaminases has been widely examined, one such limitation is the fact that the equilibrium constant for the reaction is near unity. Therefore, a shift in this equilibrium is necessary for the reaction to be synthetically useful. A number of approaches to shift the equilibrium can be found in the literature.53 124135 Another method to shift the equilibrium is a modification of that previously described. Aspartate, when used as the amino donor, is converted into oxaloacetate (32) (Scheme 19.21). Because 32 is unstable, it decomposes to pyruvate (33) and thus favors product formation. However, because pyruvate is itself an a-keto acid, it must be removed, or it will serve as a substrate and be transaminated into alanine, which could potentially cause downstream processing problems. This is accomplished by including the alsS gene encoding for the enzyme acetolactate synthase (E.C. 4.1.3.18), which condenses two moles of pyruvate to form (S)-aceto-lactate (34). The (S)-acetolactate undergoes decarboxylation either spontaneously or by the enzyme acetolactate decarboxylase (E.C. 4.1.1.5) to the final by-product, UU-acetoin (35), which is meta-bolically inert. This process, for example, can be used for the production of both l- and d-2-aminobutyrate (36 and 37, respectively) (Scheme 19.21).8132 136 137... 

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)... 

Typically the level of diacetyl might be 0.10-0.15 mg/L, well above the taste threshhold level of 0.05 mg/L. The purpose of the secondary fermentation is to allow the excess acetolactate that diffused out of the yeast cells to diffuse back in and be reduced to acetoin, before it is spontaneously converted to diacetvl that secondary fermentation can take several weeks (J. Power, J.E. Siebel Sons, Personal Communication). If acetolactate decarboxylase is used it then decarboxylat.es the acetolactate to produce C07 and acetoin in... 

Besides the improvement of fermentation performance and simplification of the process, the improvement of product quality is a target for yeast strain development. Genetic modification of yeast strains and the expression of heterologous genes (e.g. acetolactate-decarboxylase) have increased the possibilities of modifying desired or undesired flavour formation. 

Acetolactate Decarboxylase Origin Bac.Brevis inrec, Bac. subtilis Novozymes Maturex ... 

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]. 

Lyases None Lipoxygenase Amino acid decarboxylase Acetolactate decarboxylase D-amino acid oxidase Aldolases Oxynitrilases L-aspartase... 

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. 

Fujii, T., Kondo, K., Shimizu, F., Sone, H., Tanaka, J., Inoue, T. (1990). Apphcation of a ribo-somal DNA integration vector in the construction of abrewCT s yeast having alpha-acetolactate decarboxylase activity. Applied and Environmental Microbiology, 56,997-1003. 

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