Phosphoenol pyruvic acid

A. Phosphoenolpyruvate.—The mechanisms of hydrolysis of phosphate esters of phosphoenol pyruvic acid (33) have been described in detail, and 0 studies confirm an earlier postulate that attack by water on the cyclic acyl phosphate (34) occurs at phosphorus and not at carbon. In the enolase reaction, the reversible interconversion of 2-phosphoglyceric acid(35)... 

The acid cleavage of a-phenylvinyl diethyl phosphate, which most probably proceeds by an ASj 2 mechanism, was found to be catalyzed by micellar sodium dodecyl sulfate (NaLS) and hexadecyl sulfonic acid (Table 8), whereas that of phosphoenol pyruvic acid was slightly inhibited by cationic and anionic surfactants (Bunton and Robinson, 1969c). The considerably greater rate enhancement by sodium dodecyl sulfate in 0-01m than in 0-10 m acid (Table 8) can reasonably be attributed... 

Some subaerial plants use a different pathway, involving carboxylation of phosphoenol pyruvic acid (PEP) instead of ribulose diphosphate (the C02 is actually transformed into bicarbonate before incorporation), which subsequently forms a C4 compound, oxaloacetic acid, instead of PGA (Fig. 1.7). Consequently such plants are termed C4 plants. The C4 path is a relatively recent evolutionary development of particular advantage in hot dry climates (see Box 1.10).The PEP cycle effectively transfers C02 to the Calvin cycle, and each cycle confers an isotopic fractionation. Some plants, the CAM plants (see Box 1.10), can use the combined PEP-Calvin cycle path (with some leakage of C02 out of the cell between the cycles) or just the Calvin cycle. The effects of these pathways on the overall isotopic fraction are reflected in the 813C values in Table 5.8. 

Of special biochemical importance are the energy-carrying compounds acetyl phosphoric acid (5.348a) and phosphoenol pyruvic acid (11.6) which release large amounts of energy on hydrolysis (Chapter 11.3). 

Malic acid is a very active intermediary product of grape metabolism. The vine contains the L-(—) malic isomer. The vine assimilates carbon dioxide in the air by a C3 mechanism (Ruflher et al., 1983). In this manner, during the dark phase of photosynthesis, the leaves and young green grapes fix CO2 on ribulose 1,5-diphosphate to produce phospho-glyceric acid, which condenses to form hexoses and may also become dehydrated into phosphoenol pyruvic acid. CO2, catalyzed by PEP carboxylase, is fixed on this acid to form oxaloacetic acid, which is, in turn, reduced into malic acid. 

Phenolic compounds derived from a simple unit to a single benzene ring are created from the condensation of erythrose 4-phosphate, an intermediary product of the pentose phosphate cycle, with phosphoenol-pyruvic acid. This biosynthetic pathway, known as the shikimic acid pathway (Figure 10.11), leads to the production of benzoic... 

The enzyme, obtained in cr3rstalline form from human and rat muscle, catalyzes a rapid transfer of high-energy phosphate from phosphoenol-pyruvic acid to ADP as the specific acceptor ... 

The shikimic acid pathway requires the C4 sugar erythrose-4-phosphate, and phosphoenol pyruvic acid (a derivative of pyruvic acid, locked in its enol form, see Figures 1.1 and 2.19) as starting materials. The route to aromatic compounds has more steps than those met earlier, and, not surprisingly, for a plant process, uses sugar derivatives as starting materials. A total of ten carbon atoms are required, four from erythrose, and six from two molecules of pyruvate one of these is later lost as CO2. The final product therefore is a C9 compound, so that such products are... 

Figure 8.1 The shikimic acid pathway from erythrose-4-phosphate and phosphoenol-pyruvic acid to phenylpyruvic acid...

In contrast to the preceding observations and conclusions, there are reports from one laboratory that the mechanism of peptide formation resembles that of protein synthesis. Cellfree preparations of B. hrevis were observed to synthesize gramicidin and tyrocidine provided that both a 140,000 X g supernatant solution and a ribosomal preparation are present (in addition to Mg+, ATP, phosphoenol-pyruvic acid, pyruvic kinase, glutathione, and amino acid mixture). The supernatant solution presumably supplies s-RNA and amino acid activating enzymes. In this system, peptide synthesis is suppressed by exposure of either the supernatant or ribosomal portions to RNase (Uemura et al., 1963)- Furthermore, neither chloramphenicol nor puromycin are capable of differentiating protein from peptide synthesis in this system the formation of each of the products is inhibited 98% by either 10 (xg/ml of the former or 100 fi.g/ml of the latter antibiotic (Okuda et al., 1964b). 

The 3-phosphoglyceric acid then undergoes an internal chemical change and releases a molecule of water to give phosphoenol pyruvic acid (PEP). The phosphoenol pyruvic acid now acted upon by a second kinase, transfers its phospho-group to a molecule of ADP... 

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