Phosphopyruvic acid

Phosphopyruvic acid triNa salt [5541-93-5] M 360.0. It is recrystd from MeOH-Et2O the salt (Ig)... 

Phosphopyruvic acid triNa salt [5541-93-5] M 360.0. It is recrystd from MeOH-Et20 the salt (lg) is dissolved in MeOH (40ml) and dry Et20 is added in excess. The white crystals are collected and dried over P205 at 20°. [B 92 952 1959]. 

Phosphoric acid also forms esters with enols, the most interesting of these is phosphopyruvic acid, in which the enolized pyruvic acid is combined with H3PO4. Very acid-labile and very alkaline-labile, it is readily split by oxidizing scents liberating phosphoric acid. 

Stage V.— Phosphopyruvic acid reacts with adenylic acid to form adenosine triphosphate and pyruvic acid, CH3.CO.COOH. 

The fixation of CO2 in carbohydrate must be reconciled with two factors (1) the C 02 must in some way enter the carboxyl group of pyruvic acid since the isotope is eventually found exclusively in carbons 3 or 4 of the glycogen (2) the formation of phosphopyruvate prior to the synthesis of D-glucose is an essential step. This conversion of pyruvate to phosphopyruvate was considered to be irreversible until Lardy and Ziegler demonstrated that this reaction can occur in extracts of rat muscle in the presence of potassium ions. 

Then, in the presence of the enzyme enolase (phosphopyruvate hydratase, EC 4.2.1.11) and as shown in Scheme 11.25, dehydration of the 2-phospho-D-glycerate (2-phosphoglycerate) occurs to produce the phosphate enol of pyruvic acid, phos-phoenolpyruvate (PEP). 

The Citric Acid Cycle (or the Tricarboxylic Acid [TCA] Cycle or the Krebsi Cycle). It will be recalled (Schemes 11.24-11.26) that the enzyme phosphoglycerate mutase (EC 5.4.2.1) acts on PGA (obtained from, e.g., fructose-1,6-bisphosphate) to produce the isomeric, 2-phosphoglycerate and that phosphopyruvate hydratase (EC 4.2.1.11) then converts the 2-phosphoglycerate to phosphoenolpyruvate. 

Polynucleotide phosphorylase can be assayed in several ways. The liberation of inorganic phosphate can be used to follow the reaction. Both disappearance of acid-soluble nucleotides and formation of acid-insoluble nucleotides have been measured. The reverse reaction in the presence of P Mabeled phosphate allows an exchange reaction, the incorporation of P into nucleotides, to be used as an assay. The exchange reaction was the first reaction of this enzyme to be discovered, and studies on the responsible enzyme led to the finding of polynucleotide synthesis. Another assay based on the reverse reaction has been devised for rapid spectrophoto-metric determinations. A polymer of adenylic acid is incubated with the phosphorylase in the presence of phosphate, phosphopyruvate, pyruvate kinase, DPNH, and lactic dehydrogenase. The formation of ADP is thus coupled with the formation of pyruvate which reacts stoichiometrically with PPNH, so that the entire reaction can be followed at 340 m/a. 

The next steps in aromatic biosynthesis have not been demonstrated enzymatically. A labile intermediate, prephenic acid, has been isolated the side chain is derived from glucose carbons in a pattern consistent with introduction of phosphopyruvate. This compound is converted to phen-ylpyruvic acid by acid and by an enzyme detected in crude extracts of E. coli. Transamination of phenylpyruvate to give phenylalanine has already been discussed. 

Phosphate is again present in an energy-rich form (namely the enol ester). It can be transferred by phosphopyruvate kinase to ADP this transfer affords pyruvic acid, which is the most important metabolite of both anaerobic and aerobic carbohydrate metabolism. 

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