Pyruvate decarboxylase sequence

All of the pyruvate decarboxylase sequences consist of subunits of about 562-610 amino acid residues, but depending on the source, the enzyme has different structures. Pyruvate decarboxylase from baker s yeast has been reported to be a tetramer, having similar subunits of about 60 kDa, whereas pyruvate decarboxylase from brewer s yeast is an 02 2 tetramer composed of different subunits having molecular weights 59 and 61 kDa, respectively [10,11]. 

Figure 5 Model of phosphorus (P) deficiency-induced physiological changes associated with the release of P-mobilizing root exudates in cluster roots of white lupin. Solid lines indicate stimulation and dotted lines inhibition of biochemical reaction sequences or mclaholic pathways in response to P deliciency. For a detailed description see Sec. 4.1. Abbreviations SS = sucrose synthase FK = fructokinase PGM = phosphoglueomutase PEP = phosphoenol pyruvate PE PC = PEP-carboxylase MDH = malate dehydrogenase ME = malic enzyme CS = citrate synthase PDC = pyruvate decarboxylase ALDH — alcohol dehydrogenase E-4-P = erythrosc-4-phosphate DAMP = dihydraxyaceConephos-phate APase = acid phosphatase.

The hypE proteins are 302-376 residues long and appear to consist of three domains. Domain 1 shows sequence identity to a domain from phosphoribosyl-aminoimida-zole synthetase which is involved in the fifth step in de novo purine biosynthesis and to a domain in thiamine phosphate kinase which is involved in the synthesis of the cofactor thiamine diphosphate (TDP). TDP is required by enzymes which cleave the bond adjacent to carbonyl groups, e.g. phosphoketolase, transketolase or pyruvate decarboxylase. Domain 2 also shows identity to a domain found in thiamine phosphate kinase. Domain 3 appears to be unique to the HypF proteins. 

The requirement for NAD+ is to reoxidize the lipoic acid carrier. It is worth mentioning that the pyruvate acetaldehyde conversion we considered at the end of the glycolytic pathway involves the same initial sequence, and pyruvate decarboxylase is another thiamine diphosphate-dependent enzyme. 

By 1998, X-ray structures had been determined for four thiamin diphosphate-dependent enzymes (1) a bacterial pyruvate oxidase,119120 (2) yeast and bacterial pyruvate decarboxylases,121 122c (3) transketolase,110123124 and (4) benzoylformate decarboxylase.1243 Tire reactions catalyzed by these enzymes are all quite different, as are the sequences of the proteins. However, the thiamin diphosphate is bound in a similar way in all of them. 

Fig. 7. Diagrams of the schemes for modifying levels of A, alcohol dehydrogenase and B, pyruvate decarboxylase activity and testing for survival of anoxia. In A, constructs contain the 35S promoter of the cauliflower mosaic virus (35S) driving expression of the cotton Adh cDNA in either the sense (Adh) or antisense (hdA) orientation, linked to the 3 termination signal of the nopaline synthase gene (Nos). Alternatively, the expression of cotton Adh cDNA is under control of the pea Adh promoter sequence (pea Adh). In B, either the 35S promoter or the pea Adh promoter is used to drive expression of the maize pyruvate decarboxylase cDNA (Pdc), linked to a Nos 3 termination sequence. Constructs are introduced into cotton via Agrobacterium tumefaciens-mediated infection of cotton. Transformed cotton callus is then assayed for its ability to survive anoxia.

Benzoylformate decarboxylase (BFD), a TPP-dependent enzyme, features a high degree of sequence similarity with a whole family of other TPP-dependent decarboxylases, among them pyruvate decarboxylase (PDC), one of the most important enzymes in metabolism. 

Protein design by site-directed mutagenesis on pyruvate decarboxylase became possible after the 3D-structure of the enzyme from Saccharomyces uvarum had become available [35], Based on sequence comparison and secondary structure prediction, the 3D-structure of the yeast enzyme served as a model for PDCZ.m. [163], The point mutations which have been introduced into the two enzymes (Tables 4 and 5) concern catalytically important residues as well as significant side-chain interactions at the domain interface of the dimer. Besides, site-directed mutagenesis offered a powerful tool to improve the car-boligase reaction of PDCZ.m. with respect to the synthesis of (P)-PAC [163,164,170]. 

The first step in the reaction sequence that converts pyruvate to carbon dioxide and acetyl-CoA is catalyzed by pyruvate dehydrogenase, as shown in Figure 19.4. This enzyme requires thiamine pyrophosphate (TPP a metabolite of vitamin Bj, or thiamine) as a coenzyme. The coenzyme is not covalently bonded to the enzyme they are held together by noncovalent interactions. Mg + is also required. We saw the action of TPP as a coenzyme in the conversion of pyruvate to acetaldehyde, catalyzed by pyruvate decarboxylase (Section 17.4). In the pyruvate dehydrogenase reaction, an a-keto acid, pyruvate, loses carbon dioxide the remaining two-carbon unit becomes covalently bonded to TPP. 

Ethanol results from the decarboxylation of pyruvate and the reduction of acetaldehyde. Yeasts and other organisms that produce ethanol use a two-step reaction sequence. First, pyruvate decarboxylase releases CO2 to make acetaldehyde. Then alcohol dehydrogenase transfers a pair of electrons from NADH to the acetaldehyde, resulting in ethanol. 

Enzymes which degrade a-keto acids to COg and aldehydes contain thiamine pyrophosphate (D 10.4.5) as coenzyme. The keto acid is added in a reversible reaction to carbon atom 2 of the thiazole ring of thiamine pyrophosphate giving an oc-hydroxy acid derivative. This compound is decarboxylated and split to an aldehyde and thiamine pyrophosphate. Figure 25 shows this sequence of reactions for the enzyme pyruvate decarboxylase which splits pyruvate to acetaldehyde and COg. 

Holloway, P. and Subden, R.E. (1993) The isolation and nucleotide sequence of the pyruvate decarboxylase gene from Kluyveromyces marxianus. Carr. Genet., 24, 274-277. 

Conway T, Osman YA, Konnan Jl, Hoffmann EM, Ingram LO (1987) Promoter and nucleotide sequences of the Zymomonas mobilis pyruvate decarboxylase. 

Neale AD, Scopes RK, Wettenhall REH, Hoogenraad NJ (1987) Nucleotide sequence of the pyruvate decarboxylase gene from Zymomonas mobilis. NucleicAcids Res 15 1753-1761... 

Nevertheless, malonyl-CoA is a major metabolite. It is an intermediate in fatty acid synthesis (see Fig. 17-12) and is formed in the peroxisomal P oxidation of odd chain-length dicarboxylic acids.703 Excess malonyl-CoA is decarboxylated in peroxisomes, and lack of the decarboxylase enzyme in mammals causes the lethal malonic aciduria.703 Some propionyl-CoA may also be metabolized by this pathway. The modified P oxidation sequence indicated on the left side of Fig. 17-3 is used in green plants and in many microorganisms. 3-Hydroxypropionyl-CoA is hydrolyzed to free P-hydroxypropionate, which is then oxidized to malonic semialdehyde and converted to acetyl-CoA by reactions that have not been completely described. Another possible pathway of propionate metabolism is the direct conversion to pyruvate via a oxidation into lactate, a mechanism that may be employed by some bacteria. Another route to lactate is through addition of water to acrylyl-CoA, the product of step a of Fig. 17-3. Tire water molecule adds in the "wrong way," the OH ion going to the a carbon instead of the P (Eq. 17-8). An enzyme with an active site similar to that of histidine ammonia-lyase (Eq. 14-48) could... 

Lysine is formed in bacteria by decarboxylation of meso-diamino-pimelic acid (Fig. 24-14). Glycine is decarboxylated oxidatively in mitochondria in a sequence requiring lipoic acid and tetrahydrofolate as well as PLP (Fig. 15-20). A methionine decarboxylase has been isolated in pure form from a fem. ° The bacterial dialkylglycine decarboxylase is both a decarboxylase and an aminotransferase which uses pyruvate as its second substrate forming a ketone and L-alanine as products (See Eq. 

Some acetogenic bacteria, which convert CO2 to acetic acid, form pyruvate for synthesis of carbohydrates, etc., by formation of formaldehyde and conversion of the latter to glycine by reversal of the PLP and lipoic acid-dependent glycine decarboxylase, a 4-protein system. The glycine is then converted to serine, pyruvate, oxaloacetate, etc. Propose a detailed pathway for this sequence. 

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