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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PEPCase activity of plants growing in soil at five P treatments with P added to obtain shoot P ranging from deficient to adequate varied from 0. The reaction was started by addition of the enzyme preparation.
The figure was created with PyMOL . Activation by Glc6P could be important during the night or at the onset of illumination before the buildup of malate that takes place during the first hour after illumination . When the concentration of inhibitor was varied at constant concentration of substrates, the experimental data were fitted to equation 3: But they are by no means redundant.
This is consistent with competition between inhibitor and activator for their binding to the enzyme. Fully expanded leaves were used for the experiments. The same solution was always obtained after repeated submissions of the data to this server. Phosphoenolpyruvate carboxylase extraction, purification and assay Plants were kept in darkness for at least 6 h prior to extraction.
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. 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.
Six of these sequences are from monocot plants and the other seven from dicot plants. Plants of maize Zea mays L.
All other chemicals of analytical grade were from standard suppliers. Each determination was performed at least in duplicate. The concentration of phosphorylated sugars increases when the Calvin cycle is active.
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. Neutral amino acids concentrations, particularly that of Gly, increase under photorespiration conditions . 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.
The standard assay medium, final volume of 0. As a consequence of this, D and K in the maize enzyme model are not as well positioned to bind the activator molecule as fosfoenolpirubato are in the amaranth enzyme model, as fosfoeno,piruvato by a rigid docking of the Gly molecule in this site not shownwhich is consistent with the A 0. The neutral amino acid binding site is not yet known because no structure with this kind of ligand has been determined so far.
These findings suggest that the binding of Glc6P is not affected by the binding of the inhibitor to this enzyme.
Data analysis Kinetic data were analyzed by nonlinear regression calculations using a commercial computing program formulated with the algorithm of Marquardt . 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: Kinetic data were analyzed by nonlinear regression calculations using a commercial computing program formulated with the algorithm of Marquardt .
The lack of activation by Gly of the dicot isoenzymes is mainly compensated by their higher affinity for the substrate PEP and their lower affinity for the inhibitor malate than those exhibited by the monocot isoenzymes. No exogenous bicarbonate was added to the assay media, so that the concentration of bicarbonate was 0.
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.
Term Bank – carboxilasa – Spanish English Dictionary
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 inhibitor . Phosphoenolpyruvate carboxylase assay and kinetic studies. Of particular interest to us is the loop analyzed in the sequence alignments of Figure 3. A rigid docking of glycine in this position not shown suggested the feasibility of binding of the activator to these residues, as we propose.
Rates in the absence of PEP were negligible.
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.
The bicarbonate concentration in an assay medium in contact with air at pH 7. EDTA ethylenediaminetetraacetic acid disodium salt was from Merck. Received February 23, Amaranth Amaranthus hypochondriacus L.
The kinetic differences between the allosteric activators acquire special relevance under conditions close to those prevailing under illumination, i. Protein was measured by the method of Bradford , using bovine serum albumin as the standard. The points in the figures are the experimentally determined values, whereas the curves are calculated from fits of these data to the appropriate equation.