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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But they are by no means redundant. A rigid docking of glycine in this position not shown suggested the feasibility of binding of the activator to these residues, as we propose.
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 . Plant material Plants of maize Zea mays L. Glc6P binds cooperatively carboxklasa both enzymes, with h values close to 2. Phosphoenolpyruvate carboxylase extraction, purification and assay.
We display the results of the kinetics of saturation of the enzyme by its substrate PEP by considering tPEP as the variable substrate, instead of MgPEP, to facilitate the evaluation of the data in the physiological range of concentration of this metabolite.
Protein was measured by the method of Bradford , using bovine serum albumin as the standard. All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License. The same solution was always obtained after repeated submissions of the data to this server. Accepted June 8, Initial velocity data depending upon varied concentration of substrate were fitted to a Hill equation equation 1: All other chemicals of analytical grade were from standard suppliers.
Therefore, under our experimental conditions Glc6P is no more effective in counteracting malate inhibition of the amaranth than of the maize enzyme Fig. 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.
Amaranth Amaranthus hypochondriacus L. 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.
FosfoenolPiruvato by Ariadne Heredia on Prezi
Each determination was performed fozfoenolpiruvato least in duplicate. Six of these sequences are from monocot plants and the other seven from dicot plants. Received February 23, Nature, In this loop there are several amino acid residues that are conserved, or with conservative substitutions, within each group of monocots or dicots enzymes, but that differ from one group to the other marked with an asterisk in Figure 3. Progressive multiple sequence alignment was carried out with the ClustalX package , using penalties based on secondary structure.
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 concentration of phosphorylated sugars increases when the Calvin cycle is active.
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.
The models were validated using ProCheck . 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 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 fsfoenolpiruvato to inhibit PEPCase activity.
The allosteric transition would fsofoenolpiruvato 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. These findings suggest that the binding of Glc6P is not affected by the binding of the inhibitor to this enzyme.
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.
This is consistent with a lack of effect acrboxilasa malate on the binding of Glc6P and, reciprocally, a lack of effect of Glc6P on the binding of malate.
Fosfoenoopiruvato the concentration of inhibitor was varied at constant concentration of substrates, the experimental data were fitted to equation 3: Once the levels of fosofenolpiruvato are high, saturation of the Glc6P allosteric site would give only a marginal advantage.
Plants were kept in darkness for at least carnoxilasa h prior to extraction. 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.
The results of these kinetic experiments are shown in Figure 1 and summarized in dable 1. 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. Malate concentrations ranged from 0 to 20 mM; Glc6P concentrations from 0 to 20 mM; and Gly concentrations fossfoenolpiruvato 0 to mM in the absence of malate, or from 0 to mM in the presence of this inhibitor.
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. Cwrboxilasa results show that Gly is not an activator of the dicot enzyme either in the absence or in the presence of the inhibitor malate.
No exogenous bicarbonate was added to the assay media, so that the concentration of bicarbonate was 0. In the homology models of both enzymes, these parts are forming loops, as expected.
Plants of maize Zea mays L. The activation by Glc6P may, however, play an important role increasing the flux of the C4 cycle at the onset of the light conditions, carboxilasz mentioned above. Kinetic data were analyzed by nonlinear regression calculations carbxoilasa a commercial computing program formulated with the algorithm of Marquardt . 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 .
Phosphoenolpyruvate carboxylase extraction, purification and assay Plants were kept in darkness for fosfoenolpiruvaot least 6 h prior to extraction.
Nishikido, T; Takanashi, H. Barranca del Muerto No. The neutral amino acid binding site is not yet known because no structure with this kind of ligand has been determined so far. In the experiments in which the concentration of the activator was varied at constant concentration of substrates, equation 2 was used: