Pyruvic acid decarboxylase

The changes in a-ketoglutarate decarboxylase and pyruvic acid decarboxylase activities are not the only biochemical alterations observed in thiamine deficiency. The activities of some other enzymes were found to be altered, for example, erythrocyte transke-tolase and adenosine-5 -phosphatase activities are decreased in chicken brain. 

In general, pyruvate decarboxylase (EC 4.1.1.1) catalyzes the decarboxylation of a 2-oxocar-boxylic acid to give the corresponding aldehyde6. Using pyruvic acid, the intermediately formed enzyme-substrate complex can add an acetyl unit to acetaldehyde already present in the reaction mixture, to give optically active acetoin (l-hydroxy-2-butanone)4 26. Although the formation of... 

Mutation of the dihydrolipoate reductase component impairs decarboxylation of branched-chain a-keto acids, of pyruvate, and of a-ketoglutarate. In intermittent branched-chain ketonuria, the a-keto acid decarboxylase retains some activity, and symptoms occur later in life. The impaired enzyme in isovaleric acidemia is isovaleryl-CoA dehydrogenase (reaction 3, Figure 30-19). Vomiting, acidosis, and coma follow ingestion of excess protein. Accumulated... 

These enzymes catalyse the non-hydrolytic cleavage of bonds in a substrate to remove specific functional groups. Examples include decarboxylases, which remove carboxylic acid groups as carbon dioxide, dehydrases, which remove water, and aldolases. The decarboxylation of pyruvic acid (10.60) to form acetaldehyde (10.61) takes place in the presence of pyruvic decarboxylase (Scheme 10.13), which requires the presence of thiamine pyrophosphate and magnesium ions for activity. 

Various thiamine diphosphate (ThDP)-dependent a-keto acid decarboxylases have been described as catalyzing C-C bond formation and/or cleavage [48]. Extensive work has already been conducted on transketolase (TK) and pyruvate decarboxylase (PDC) from different sources [49]. Here attention should be drawn to some concepts based on the investigation of reactions catalyzed by the enzymes... 

Figure B.l. Mechanism for the conversion of pyruvic acid to acetaldehyde and CO2 by pyruvate decarboxylase.

Figure 13.8 Pathway for metabolism of citrate by Leuconostoc spp. and S. lactis subsp. diacetylactis. (1) Citrate permease, (2) citrate lyase, (3) oxaloacetic acid decarboxylase, (4) pyruvate decarboxylase, (5) a-acetolactate synthetase, (6) a-acetolactate carboxylase, (7) diacetyl synthetase, (8) diacetyl reductase, and (9) acetoin reductase.

Diseases and disorders resulting from a deficiency of thiamine include beriben, opisthotonos (in birds), polyneuritis, hyperesthesia, bradycardia, and edema. Rather than a specific disease, beriberi may be described as a clinical state resulting from a thiamine deficiency. In body cells, thiamine pyrophosphate is required for removing carbon dioxide from various substances, including pyruvic acid. Actually, this is accomplished by a decarboxylase of which thiamine pyrophosphate is a part. Where... 

EC 1.11.1.7) (68) and diphenol oxidase (EC 1.10.3.1) (69) have been identified. The potential role of pyruvic decarboxylase (EC 4.1.1.1) catalyzed reaction as a source of acetaldehyde and other aldehydes in juice was discussed (70). Raymond et al. (71) isolated the decarboxylase from orange juice sections and demonstrated that only 10 to 15% of the enzyme was in an active form. Since the purified enzyme was only active with pyruvic acid and 2-ketobutyric acid of the series of 2-ketoacids examined, they (71) concluded that the direct contribution of orange pyruvic decarboxylase to the orange volatile profile was limited to acetaldehyde and possibly propionaldehyde. 

Biological compounds with long chains of carbon atoms are broken down into molecules with shorter chains by the breaking of carbon-carbon bonds. This commonly occurs by the elimination of -C02H groups from carboxylic acids. For example, pyruvic decarboxylase enzyme acts upon pyruvic acid,... 

The a-keto acid decarboxylases such as pyruvate (E.C. 4.1.1.1) and benzoyl formate (E.C. 4.1.1.7) decarboxylases are a thiamine pyrophosphate (TPP)-dependent group of enzymes, which in addition to nonoxidatively decarboxylating their substrates, catalyze a carboligation reaction forming a C-C bond leading to the formation of a-hydroxy ketones.269-270 The hydroxy ketone (R)-phenylacetylcarbinol (55), a precursor to L-ephedrine (56), has been synthesized with pyruvate decarboxylase (Scheme 19.35). BASF scientists have made mutations in the pyruvate decarboxylase from Zymomonas mobilis to make the enzyme more resistant than the wild-type enzyme to inactivation by acetaldehyde for the preparation of chiral phenylacetylcarbinols.271... 

Amino acids NAD(P)H Pyridoxamine 5 -phosphate Pyruvate Amines Pyridoxal 5-phosphate dependent enzymes Dehydrogenases Transaminases Pyridoxal 5-phosphate dependent enzymes Amino acid decarboxylases... 

Calculate the entropy change for the conversion of pyruvic acid (CH3COCOOH) into acetaldehyde and C02 by the enzyme pyruvate decarboxylase at 25°C and 100 atm. 

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)... 

Aspartate undergoes /3-decarboxylation to /S-alanine unlike most amino acid decarboxylases, aspartate decarboxylase is not pyridoxal phosphate-dependent, but has a catalytic pyruvate residue, derived by postsynthetic modification of a serine residue (Section 9.8.1). Pantothenic acid results from the formation of a peptide bond between /3-alanine and pantoic acid. 

It is not known to what extent taurine may be a dietary essential for human beings. There is little cysteine sulfinic acid decarboxylase activity in the human liver and, like the cat, loading doses of methionine and cysteine do not result in any significant increase in plasma taurine. This may be because cysteine sulfinic acid can also undergo transamination to /3-sulfhydryl pyruvate, which then loses sulfur dioxide nonenzymically to form pyruvate, thus regulating the amount of taurine that is formed from cysteine. There is no evidence of the development of any taurine deficiency disease under normal conditions. 

Branched-Chain Oxo-acid Decarboxylase and Maple Syrup Urine Disease The third oxo-add dehydrogenase catalyzes the oxidative decarboxylation of the branched-chain oxo-acids that arise from the transamination of the branched-chain amino acids, leucine, isoleuctne, emd vtdine. It has a similEU subunit composition to pyruvate and 2-oxoglutarate dehydrogenases, and the E3 subunit (dihydrolipoyl dehydrogenase) is the stune protein as in the other two multienzyme complexes. Genetic lack of this enzyme causes maple syrup urine disease, so-called because the bremched-chain oxo-acids that are excreted in the urine have a smell reminiscent of maple syrup. 

The biogenesis of solerone 1 and related compounds was successfully rationalized by biomimetic model reactions. As key step we established the pyruvate decarboxylase catalyzed acyloin condensation of pyruvic acid with ethyl 4-oxobutanoate 4 or ethyl 2-oxoglutarate 3 with acetaldehyde. The importance of the ethyl ester function in 3 and 4 serving as substrates for the enzymatic formation of a-hydroxy ketones 5 and 6 was demonstrated. The identification of six yet unknown sherry compounds including acyloins 5 and 6, which have been synthesized for the first time, confirmed the relevance of the biosynthetic pathway. Application of MDGC-MS allowed the enantiodifferentiation of a-ketols and related lactones in complex sherry samples and disclosed details of their biogenetic relationship. 

After biochemical conversion of glucose to pyruvic acid intermediate, the next step in ethanol synthesis is nonoxidative decarboxylation and acetaldehyde formation catalyzed by a native decarboxylase, and then acetaldehyde reduction to ethanol catalyzed by a native dehydrogenase. 

Models were also reported for the pyruvyl-dependent a-amino acid decarboxylases Using a variety of amino acids along with pyruvate or pyruvamide or ethyl pyruvate in DMF leads to decarboxylation via the imine. The putative azomethine ylide... 

It may be observed that, for the cycle to revolve, a supply of oxaloacetic acid is required with which the acetyl-CoA can react. Of course, oxaloacetic acid is being constantly re-formed as each revolution of the cycle is completed, but, nonetheless, it is not surprising to find that many cells, especially in bacteria, take precautions against running out of so essential a primer by having an alternative source of oxaloacetic acid. The alternative source is provided by an enzyme, oxaloacetic decarboxylase which catalyses the direct fixing of carbon dioxide on to pyruvic acid to form oxaloacetic acid as in equation (24) ... 

Although most amino acid decarboxylases use PLP as a cofactor, a number of decarboxylases use covalently bound pyruvate instead (722, 123). The pyruvate-dependent enzyme consists of two types of chains. The pyruvoyl cofactor is formed by the cleavage of a Ser-Ser linkage in a single-chain precursor and is bound as an amide to the N-terminus of one polypeptide chain. 

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