FosfoenolPiruvato. AH Universidad del mar. La enzima fosfoenolpiruvato carboxilasa. Fecha de consulta: 13/Noviembre/ Consultado. En este trabajo, investigamos la compleja regulación alostérica de la formas no fosforiladas de las isoenzimas fotosintéticas de la fosfoenolpiruvato carboxilasa. Acetil-CoA = acetil-coenzima A, MDH = malato deshidrogenasa, OAA = oxalacetato, PEP = fosfoenolpiruvato, PEPC = fosfoenolpiruvato carboxilasa piruvato y.
|Published (Last):||16 December 2004|
|PDF File Size:||12.93 Mb|
|ePub File Size:||2.4 Mb|
|Price:||Free* [*Free Regsitration Required]|
Phosphoenolpyruvate carboxylase assay and kinetic studies. The standard assay medium, final volume of 0.
Six of these sequences are from monocot plants and the other seven from dicot plants. These two limiting concentrations of tPEP are close to those existing in the cytosol of the mesophyll cells during the dark and light periods, respectively [22, 23]. The best fits were determined by the relative fit error, error of the constants and absence of significant correlation between the residuals, and other relevant variables like observed velocities, substrate concentration and data number.
Nature, In a broad range of P concentrations in nutrient solutions with P added to obtain shoot P ranging from deficient to near toxicitythe enzyme activity and citrate release were reduced to almost undetectable levels when shoot P was increased to 0. The bicarbonate concentration in an assay medium in contact with air at pH 7.
Malate concentrations ranged from 0 to 20 mM; Glc6P concentrations from 0 to 20 mM; and Gly concentrations from 0 to mM in the absence of malate, or from 0 to mM in the presence of this inhibitor.
These results show that Gly is not an activator of the dicot enzyme either in the absence or in the presence of the inhibitor malate.
Although the S 0. EDTA ethylenediaminetetraacetic acid disodium salt was from Merck. The results indicate that in vitro PEPCase activity does not significantly change with the range of shoot P from deficient to adequate, and suggest that the mechanism associated with citrate excretion might be impaired at P concentrations lower than those required to inhibit PEPCase activity.
In the homology models of both enzymes, these parts are forming loops, as expected. Photorespiration surely follows the buildup of malate during the day because of a decrease of the C4 cycle flux, a decrease due to both PEPC inhibition by the increased malate concentration and depletion of the available CO 2 by a very active Calvin cycle.
Gly has been found to be much more effective than Fosfoemolpiruvato in this respect under conditions close to those existing in vivo during the light period fosfoeolpiruvato. These results indicate that the binding of malate and that of Glc6P to the amaranth enzyme are competitive.
Both types of isoenzymes also differ in their affinity for the substrate PEP, the activator Glc6P and the inhibitor malate. Plant material Plants of maize Zea mays L. The lack of activation by Gly of the dicot isoenzymes is mainly compensated by their fosfoenolpiruvago affinity for the substrate PEP and their lower affinity for the inhibitor malate than those exhibited by the monocot isoenzymes.
Nishikido, T; Takanashi, H. The concentration of phosphorylated sugars increases when the Calvin cycle is active. The allosteric transition would not occur in the amaranth enzyme, thus accounting for the huge differences between the amaranth and the maize enzymes in their degree of activation carboxilasx at saturation by Gly.
Term Bank – carboxilasa – Spanish English Dictionary
It has been propoosed that one of the functions of foxfoenolpiruvato enzyme phosphoenolpyruvate carboxylase PEPCase in the roots of white lupines consists in providing the carbon required to support the significant quantity of citrate that is excreted by P-starved plants.
Sequence alignments and homology model building. Rates in the absence of PEP were negligible. Phosphoenolpyruvate carboxylase extraction, purification and assay Plants were kept in darkness for at least 6 h prior to extraction.
FosfoenolPiruvato by Ariadne Heredia on Prezi
Plants were kept in darkness for at least 6 h prior to extraction. The figure was fosfosnolpiruvato with PyMOL . Amaranth Amaranthus hypochondriacus L. These findings suggest that the binding of Glc6P is not affected by the binding of the inhibitor to this enzyme.
When the concentration of inhibitor was varied at constant concentration of substrates, the experimental carboxioasa were fitted to equation 3: This is consistent with competition between inhibitor and activator for their binding to the enzyme. The activation by Glc6P may, however, play an important role increasing the fosfoenolpiruvayo of the C4 cycle at the onset of the light conditions, as mentioned above.
The points in the figures are the experimentally determined values, whereas the curves are calculated from fits of these data to the appropriate equation. The reaction was started by addition of the enzyme preparation. The kinetic differences between the allosteric activators acquire special relevance under conditions close to those prevailing under illumination, i.
Each determination was performed at least in duplicate.
The differences between the two enzymes in the degree of cooperativity in the binding of PEP in the presence of a high malate concentration are fosfoenolpiruvati full agreement with their differences in malate affinity. All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License.
When near physiological concentrations were used, Glc6P was very ineffective in overcoming malate inhibition . Accepted June 8,