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.
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Therefore, the two kinds of activators act as metabolic signals that indicate the necessity of increasing the flux through the C4 cycle, in order to keep pace with the flux rate of the Calvin cycle in the case of Glc6P, or to increase the supply of CO 2 to the bundle sheath cells to prevent photorespiration, in the case of Gly.
Fully expanded leaves were used for the experiments. Both types of isoenzymes also differ in their affinity for the substrate PEP, the activator Glc6P and the inhibitor malate.
Gly has been found to be much more effective than Glc6P in this respect under conditions close to those existing in vivo during the light period . Activation by Gly helps in increasing the flux through the C4 pathway by effectively counteracting the inhibitory effects of malate, and, therefore, it helps in increasing the concentrations of CO2 in the bundle sheet cells thus overcoming photorespiration. 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 achieved at saturation by Gly.
Amaranth Amaranthus hypochondriacus L. Rates in the absence of PEP were negligible. The standard assay medium, final volume of 0. 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 models were validated using ProCheck . Received February 23, In the experiments in which the concentration of the activator was varied at constant concentration of substrates, equation 2 was used: 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. Six of these sequences are from monocot plants and the other seven from dicot plants.
Phosphoenolpyruvate carboxylase assay and kinetic studies.
These results indicate that the binding fosfoenoloiruvato malate and that of Glc6P to the amaranth enzyme are competitive. As a consequence of this, D and K in the maize enzyme model are not as well positioned to bind the activator molecule as they are in the amaranth enzyme model, as indicated by a rigid docking of the Gly molecule in this site not shownwhich is consistent with the A 0.
All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License. Introduction In leaves of C4 plants the initial reaction in the assimilation pathway of atmospheric CO 2 is the essentially irreversible carboxylation of phospho eno lpyruvate PEP by phospho eno lpyruvate carboxylase orthophosphate: When near physiological concentrations were used, Glc6P was very ineffective in overcoming malate inhibition .
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 in full agreement with their differences in malate affinity. The concentration of phosphorylated sugars increases when the Calvin cycle is active.
No exogenous bicarbonate was added to the assay media, so that the concentration of bicarbonate was 0. Accepted June 8, Therefore, under our experimental conditions Glc6P is no more effective in counteracting malate inhibition of the amaranth than of the maize enzyme Fig.
It has been propoosed that one of the functions of the 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.
FosfoenolPiruvato by Ariadne Heredia on Prezi
The lack of activation by Gly of the fosfoenoliruvato isoenzymes is mainly compensated by their higher affinity for the substrate PEP and their lower affinity for the inhibitor malate than those exhibited by fosfoebolpiruvato monocot isoenzymes. In leaves of C4 plants the initial reaction in the assimilation pathway of atmospheric CO 2 is the essentially irreversible carboxylation of phospho eno lpyruvate PEP by phospho eno lpyruvate carboxylase orthophosphate: Plants of maize Zea mays L.
The overall identity among monocot isoenzymes ranged from 80 to Phosphoenolpyruvate carboxylase extraction, purification and assay Plants were kept in darkness for at least 6 h prior to extraction. We tested now the relative contribution of the two kinds of activators in relieving malate inhibition of the two C4 isoenzymes at the tPEP concentration existing during the night, 0.
But they are by no means redundant.
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 fosfoenolpiruvafo P concentrations lower than those required to inhibit PEPCase activity.
One unit of PEPC is defined as the amount of enzyme needed to catalyze the formation of 1 umol of oxalacetate per min under our experimental conditions.
Kinetic data were analyzed by nonlinear regression calculations using a commercial computing program formulated with the algorithm of Marquardt .
EDTA ethylenediaminetetraacetic acid disodium salt was from Merck. Data analysis Kinetic data were analyzed by nonlinear regression calculations using a commercial computing program formulated with the algorithm tosfoenolpiruvato Marquardt . These findings suggest that the binding of Glc6P is not affected by the binding of the inhibitor to this enzyme. Once the levels of malate are high, saturation of the Glc6P allosteric site would give only a marginal advantage.
Nature, The figure was created with PyMOL . When the concentration of inhibitor was varied at constant concentration of substrates, the experimental data were fitted to equation 3: Although the S 0.
Term Bank – carboxilasa – Spanish English Dictionary
Plants fosfoenolpkruvato kept in darkness for at least 6 h prior to extraction. A rigid docking of carboxllasa in this position not shown suggested the feasibility of binding of the activator to these residues, as we propose. 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.
Initial velocity data depending upon varied concentration of substrate were fitted to a Hill equation equation 1: While Glc6P is unable to revert the inhibition caused by a physiological concentration of malate, Gly can produce an enzyme almost as active than that in the absence of the fosfoeno,piruvato . The same solution was always obtained after repeated submissions of the data to this server.
The bicarbonate concentration in an assay medium in contact with air at pH 7. 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.
Activation fosfoenolpiruvatto Glc6P could be important during the night or at the fosfoenolpiruuvato of illumination before the buildup of malate that takes place during the first hour after illumination .
In the homology models of both enzymes, these parts are forming loops, as expected.