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Query: EC:4.1.1.32 (phosphoenolpyruvate carboxykinase)
 4,204 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of low concentrations of phosphate (low-P) on soluble protein content, the activities of 12 different enzymes, and the rates of photosynthesis and respiration on the basis of leaf area were investigated in maize (Zea mays L.) leaves 16 to 24 days after planting (DAP). With low-P treatment, a drastic decrease in the rate of photosynthesis to only 6% of the maximum rate in control plants was observed by 24 DAP. Low-P treatment had almost no effect on the rate of respiration until 21 DAP, but then the rate of respiration decreased progressively to about 55% of the maximum rate in control plants. The soluble protein content in low-P plants decreased to 56% of the maximum content in control plants. The changes in the activities of enzymes in low-P plants showed several different patterns. The activities of pyruvate, orthophosphate dikinase, 3-phosphoglycerate kinase, phosphoenolpyruvate carboxylase (PEPC), ribulose 1,5-bisphosphate carboxylase, fructose 1,6-bisphosphate aldolase, catalase, phosphohexose isomerase, chloroplastic fructose 1,6-bisphosphatase, and ADP-glucose-pyrophosphorylase decreased steadily from 85 to 100% of the maximum activity found in 18- to 21-day-old control plants (V(max)) to 30 to 70% of V(max). The activity of sucrose phosphate synthase remained virtually constant at approximately 85 to 100% of V(max). The activity of UDP-glucose-pyrophosphorylase remained almost constant up to 21 DAP and then decreased to 80% of V(max) by 24 DAP. The activity of cytochrome c oxidase increased slightly up to 21 DAP but then decreased to 50% of V(max) by 24 DAP. As indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of soluble proteins, the subunit of PEPC stained less intensely in 24-d-old low-P plants. The possibility is discussed that during low-P treatment there is selective degradation of PEPC without a concomitant degradation of sucrose phosphate synthase, both of which are known to be localized in the cytoplasmic compartment of mesophyll cells.
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PMID:Phosphate Deficiency in Maize : III. Changes in Enzyme Activities during the Course of Phosphate Deprivation. 1666 91

Temperature is a strong selective force on the evolution of proteins due to its effects on higher orders of protein structure and, thereby, on critical protein functions like ligand binding and catalysis. Comparisons among orthologous proteins from differently thermally adapted species show consistent patterns of adaptive variation in function, but few studies have examined functional adaptation among multiple structural families of proteins. Thus, with our present state of knowledge, it is difficult to predict what fraction of the proteome will exhibit adaptive variation in the face of temperature increases of a few to several degrees Celsius, that is, temperature increases of the magnitude predicted by models of global warming. Here, we compared orthologous enzymes of the warm-adapted Mediterranean mussel Mytilus galloprovincialis and the cold-adapted Mytilus trossulus, a native of the North Pacific Ocean, species whose physiologies exhibit significantly different responses to temperature. We measured the effects of temperature on the kinetics (Michaelis-Menten constant-K(m)) of five enzymes that are important for ATP generation and that represent distinct protein structural families. Among phosphoglucomutase (PGM), phosphoglucose isomerase (PGI), pyruvate kinase (PK), phosphoenolpyruvate carboxykinase (GTP) (PEPCK), and isocitrate dehydrogenase (NADP) (IDH), only IDH orthologs showed significantly different thermal responses of K(m) between the two species. The K(m) of isocitrate of M. galloprovincialis-IDH was intrinsically lower and more thermally stable than that of M. trossulus-IDH and thus had higher substrate affinity at high temperatures. Two amino acid substitutions account for the functional differences between IDH orthologs, one of which allows for more hydrogen bonds to form near the mobile region of the active site in M. galloprovincialis-IDH. Taken together, our findings cast light on the targets of adaptive evolution in the context of climate change; only a minority of proteins might adapt to small changes in temperature, and these adaptations may involve only small changes in sequence.
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PMID:Functional determinants of temperature adaptation in enzymes of cold- versus warm-adapted mussels (Genus Mytilus). 2249 Oct 35

Enzymes representative of, and related to, the pentose phosphate pathway, glycolysis, and the tricarboxylic acid cycle have been demonstrated in supernatant and lamellar fractions of Anabaena cylindrica cultured in the presence of atmospheric nitrogen, ammonia, nitrite, and nitrate. Nitrogen-fixing and ammonia-assimilating algae contained essentially similar levels of most enzymes tested, with the notable exception of glyceraldehyde-3-phosphate dehydrogenase which showed increased NADPH-linked activity with concomitant diminution of NADH-linked activity when ammonia was supplied. The provision of nitrite or nitrate caused significant enhancements of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and the related hexokinase and phosphohexoisomerase. Reduced activities of pyruvate kinase, malate dehydrogenase, phosphoenolpyruvate carboxylase, and both NADH and NADPH oxidoreductases were recorded for nitrate-grown alga.The stimulation of the pentose phosphate pathway, at the partial expense of glycolysis and the tricarboxylic acid cycle, in algae cultured with nitrite and nitrate was interpreted to be due to additional NADPH requirements imposed by induced nitrite reductase. Modification of the pyridine nucleotide linkage of glyceraldehyde-3-phosphate dehydrogenase and the oxidoreductases was attributed to diversion of reductant to nitrite and nitrate reductases and nitrogenase. The results are considered to indicate regulation of blue-green algal metabolism determined by the availability of pyridine nucleotides.
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PMID:The influence of inorganic nitrogen supply on carbohydrate and related metabolism in the blue-green alga, Anabaena cylindrica Lemm. 2445 90


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