Presence of cold sensitive PEP synthetase enzyme is a characteristic feature of
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Explanation:
ABSTRACT
Phosphoenolpyruvate synthetase (PpsA) was purified from the hyperthermophilic archaeon Pyrococcus furiosus. This enzyme catalyzes the conversion of pyruvate and ATP to phosphoenolpyruvate (PEP), AMP, and phosphate and is thought to function in gluconeogenesis. PpsA has a subunit molecular mass of 92 kDa and contains one calcium and one phosphorus atom per subunit. The active form has a molecular mass of 690 ± 20 kDa and is assumed to be octomeric, while approximately 30% of the protein is purified as a large (∼1.6 MDa) complex that is not active. The apparent Km values and catalytic efficiencies for the substrates pyruvate and ATP (at 80°C, pH 8.4) were 0.11 mM and 1.43 × 104 mM−1 · s−1 and 0.39 mM and 3.40 × 103 mM−1 · s−1, respectively. Maximal activity was measured at pH 9.0 (at 80°C) and at 90°C (at pH 8.4). The enzyme also catalyzed the reverse reaction, but the catalytic efficiency with PEP was very low [kcat/Km = 32 (mM · s)−1]. In contrast to several other nucleotide-dependent enzymes from P. furiosus, PpsA has an absolute specificity for ATP as the phosphate-donating substrate. This is the first PpsA from a nonmethanogenic archaeon to be biochemically characterized. Its kinetic properties are consistent with a role in gluconeogenesis, although its relatively high cellular concentration (∼5% of the cytoplasmic protein) suggests an additional function possibly related to energy spilling. It is not known whether interconversion between the smaller, active and larger, inactive forms of the enzyme has any functional role.
A number of unique microorganisms that thrive at temperatures of 90°C or higher have been isolated in the last 2 decades. One of the best studied of these so-called hyperthermophiles is the anaerobic archaeon Pyrococcus furiosus, which grows optimally at 100°C by the fermentation of carbohydrates and peptides (15). The organism uses a modified Embden-Meyerhof glycolytic pathway that contains several novel enzymes (13, 23). For example, both hexokinase and phosphofructokinase are ADP- rather than ATP-dependent enzymes (24, 48). In addition, the expected glyceraldehyde-3-phosphate dehydrogenase and phosphoglycerate kinase enzymes, which would convert glyceraldehyde-3-phosphate to 3-phosphoglycerate with the concomitant phosphorylation of ADP to ATP and reduction of NAD+ to NADH, appear to be replaced by a single enzyme, glyceraldehyde-3-phosphate:ferredoxin oxidoreductase (GAPOR). GAPOR oxidizes glyceraldehyde-3-phosphate directly to 3-phosphoglycerate and uses ferredoxin rather than NAD+ as the electron acceptor. Purified GAPOR is a unique tungsten-containing enzyme that has no known analog in mesophilic archaea or bacteria (31). Another unusual step in glucose catabolism includes the conversion of acetyl coenzyme A (acetyl-CoA) to acetate. In anaerobic bacteria, this is a two-step process via acetyl phosphate catalyzed by phosphotransacetylase and acetate kinase. In P. furiosus, however, these two enzymes are replaced by acetyl-CoA synthetase, which converts acetyl-CoA directly to acetate and phosphorylates ADP to ATP (29). Other enzymes involved in glucose oxidation that have been purified from Pyrococcus species include pyruvate:ferredoxin oxidoreductase (4), enolase (36), and triosephosphate isomerase (25)
Presence of cold sensitive PEP synthase enzyme is a charecteristic feature of most Organisms which perform glycolysis.
Explanation:
- The glycolysis is a process which takes place iñ the cytoplasm of the cell and it forms pyruvic acid as a byproduct.
- It stands for Phosphoenolpyruvate. It helps in the last step of glycolysis and it forms pyruvic acid.
- The glycolysis is a common pathway for the aerobic and anaerobic respiration and it takes place even in the absence of oxygen. Hence it is a common metabolic process. It takes place even in anaerobic bacteria.
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