Phosphoenolpyruvate synthetase enzyme

The problem of focusing phosphorylation free energy is elegantly solved in the mechanisms of action of phosphoenolpyruvate synthetase and pyruvate phosphate dikinase. Phosphohistidyl residues are generated at the active sites of these enzymes by pyrophosphorylation of active site histidines, followed by hydrolysis... 

Gene activated Lipoprotein lipase fatty acid transporter protein adipocyte fatty acid binding protein acyl-CoA synthetase malic enzyme GLUT-4 glucose transporter phosphoenolpyruvate carboxykinase... 

This enzyme [EC 4.1.2.16] (also known as phospho-2-dehydro-3-deoxyoctonate aldolase, phospho-2-keto-3-deoxyoctonate aldolase, and 3-deoxy-D-manno-octulo-sonic acid 8-phosphate synthetase) catalyzes the reaction of 2-dehydro-3-deoxy-D-octonate 8-phosphate and orthophosphate to produce phosphoenolpyruvate, D-arabinose 5-phosphate, and water. 

Available evidence (14,15) favors the pathway for pyruvate kinase by way of phosphorylation of pyruvate enol. Furthermore, J. Knowles and his coworkers (16,17), using chiral thiophosphates and chiral (160,170,180) phosphate have shown that pyruvate kinase transfers phosphate from phosphoenolpyruvate to ADP with stereochemical inversion at phosphorus. Since monomeric metaphosphate is presumably planar, a chemical reaction by way of that ion should proceed with racemization. In the active site of an enzyme, however, all components might be held so rigidly that racemization need not occur. Furthermore, no information is yet available on the detailed mechanism of reactions catalyzed by cytidine synthetase our own experiments, designed to distinguish among the mechanisms here discussed, are as yet incomplete. 

Biotin acts to induce glucokinase, phosphofructokinase, and pyruvate kinase (key enzymes of glycolysis), phosphoenolpyruvate carboxykinase (a key enzyme of gluconeogenesis), and holocarboxylase synthetase, acting via a cell-surface receptor linked to formation of cGMP and increased activity of RNA polymerase. The activity of holocarboxylase synthetase (Section 11.2.2) falls in experimental biotin deficiency and increases with a parallel increase in... 

Comprehensive Biological Catalysis—a Mechanistic Reference Volume has recently been published. The fiiU contents list (approximate number of references in parentheses) is as follows S-adenosylmethionine-dependent methyltransferases (110) prenyl transfer and the enzymes of terpenoid and steroid biosynthesis (330) glycosyl transfer (800) mechanism of folate-requiring enzymes in one-carbon metabohsm (260) hydride and alkyl group shifts in the reactions of aldehydes and ketones (150) phosphoenolpyruvate as an electrophile carboxyvinyl transfer reactions (140) physical organic chemistry of acyl transfer reactions (220) catalytic mechanisms of the aspartic proteinases (90) the serine proteinases (135) cysteine proteinases (350) zinc proteinases (200) esterases and lipases (160) reactions of carbon at the carbon dioxide level of oxidation (390) transfer of the POj group (230) phosphate diesterases and triesterases (160) ribozymes (70) catalysis of tRNA aminoacylation by class I and class II aminoacyl-tRNA synthetases (220) thio-disulfide exchange of divalent sulfirr (150) and sulfotransferases (50). 

Scheme L Synthesis of a2,64inked sialyl-N-acetyllactosamine using a one-pot multi-enzyme system with in situ regeneration of CMP-Neu5Ac. Abbreviations for enzymes CSS, CMP-sialic acid synthetase NMK, nucleoside monophosphate kinase PK, pyruvate kinase PPase, pyrophosphatase. Abbreviations for compounds PEP, phosphoenolpyruvate ADP, adenosine 5 -diphosphate ATP, adenosine 5 -triphosphate CMP, cytidine 5-monophosphate CDP, cytidine 5 -diphosphate CTP, cytidine 5-triphosphate LacNAc, N-acetyllactosamine NeuSAc, N-acetylneuraminic acid PPi, inorganic pyrophosphate.

Synthesis of iV-acetylneuraminic acid (Neu5Ac) in vivo is catalyzed by Neu5Ac synthetase (EC 4.1.3.19) through the irreversible condensation of phosphoenolpyruvate (PEP) and A/-acetylmannosamine (15) (Scheme 2) [30-32], This enzyme has not yet been isolated and its catalytic activity might be interesting field for exploration. 

The 3-deoxy-D-ara6mo-2-heptulosonic acid 7-phosphate (DAHP) synthetase (EC 4.1.2.15) is an enzyme involved in the shikimic pathway of aromatic amino acids biosynthesis in bacteria and plants, where catalyzes the construction of 3-deoxy-D-ara6/ o-2-heptulosonic acid 7-phosphate from phosphoenolpyruvate and D-erythrose 4-phosphate [6]. Although 3-deoxy-D-ara6/H0-2-heptulosonic acid 7-phosphate (DAHP) synthetase has not been widely investigated it has been employed for the DAHP synthesis on preparative scale from D-fructose in multienzyme system [68], This one-pot synthesis was subsequently even more simplified by the results of further studies which indicated that it was more efficient and economical to use the whole cells containing a DAHP synthetase plasmid [69]. 

Note 1. Abbreviations used are AD, aminidase C, carboxylase DH, dehydro nase Ez, enzyme/enzymes ER, endoplasmic reticulum Fa, fatty add H, hexo-/hexose L, lyase P, phosphatate Pase, phosphatase K, kinase PEP, phosphoenolpyruvate PPP, pentose phosphate pathway NM/D/TP, nucleoside mono/di/lriphosphate NTF, nucleotidyltransfra-ase S, synthese/synthetase TF, transferase. 

A multigram enzymic synthesis of KDO-8-phosphate has been devised D-arablnose-5-phosphate is prepared by hexokinase action on the sugar, and is then condensed with phosphoenolpyruvate using KDO-8-phosphate synthetase. The ATP required for the hexokinase reaction is regenerated from phosphoenolpyruvate using pyruvate kinase.22... 

Studies on the regulation of the common pathway of aromatic biosynthesis in several micro-organisms have shown that control of the first reaction (Figure 1.2), the conversion of o-erythrose-4-phosphate (7) and phosphoenolpyruvate (8) to 3-deoxy-o-arabino-heptulosonic acid-7-phosphate (9, DAHP), catalysed by the enzyme DAHP synthetase (EC 4.1.2.15) is an important factor in the overall control of the pathway In a number of enteric bacteria this enzyme exists in multiple molecular forms each of which is under the feedback control of a specific end-product. Thus in Escherichia coli there are three DAHP synthetases (iso-enzymes), the activity and formation of which are controlled by the three aromatic amino acids The formation and activity of DAHP synthetase... 

Further support for the operation of the shikimate pathway in higher plants has been provided by studies on enzymes isolated and characterised from plant sources. DAMP synthetase activity has thus been demonstrated in extracts of several plant tissues. An enzyme preparation was also obtained from sweet potato which catalysed the formation of DAHP from D-erythrose-4-phosphate (7) and phosphoenolpyruvate (8) and had properties very similar to those enzymes isolated from bacterial sources. Nandy and Ganguli have similarly demonstrated the presence of DAHP synthetase activity in mung bean Phaseolus aureus) by showing that extracts of mung bean seedlings converted a mixture of the two substrates (7 and 8) to 3-dehydroshikimate (11). 

The carbon flow from 3-phosphoglycerate, phosphoenolpyruvate, pyruvate and acetyl-CoA. Even if the synthesis of aromatic amino acids by shikimate pathway /28,29,30,31/ and also prenyl-PP synthesis via mevalonate /32,33,34/ has been established in chloroplasts by identification of respective plastidic enzymes, it is still a matter of discussion from where PEP origins to supply DAHP synthesis of the shikimate pathway and from where pyruvate is delivered to supply the plastidic pyruvate dehydrogenase complex (for isolation see Treede and Heise, this Conference). Because phosphoglycerate mutase (PGM) to form 2-PGA from 3-PGA could not be detected in chloroplasts /35/ and acetyl-CoA is preferably synthesized from added acetate by the actetyl-CoA synthetase /36/, particularly in spinach chloroplasts, it was argued that chloroplasts are dependent on import of these substrates from the external site. Evidence for PEP formation from 3-PGA within the chloroplast could be obtained by three different approaches (D. Schulze-Siebert, A. Heintze and G. Schultz, in preparation D. Schulze-Siebert and G. Schultz, in preparation, for plastidic isoenzyme of PGM in Ricinus see /37/ and in Brassica /38/). 

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