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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The points in the figures are the experimentally determined values, whereas the curves are calculated from fits of these data to the appropriate equation. Although the S 0.

The overall identity among monocot carbixilasa ranged from 80 to Initial velocity data depending upon varied concentration of substrate were fitted to a Hill equation equation 1: Received February fosvoenolpiruvato, 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.

In the experiments in which the concentration of the activator was varied at constant concentration of substrates, equation 2 was carboxilasx The models were validated using ProCheck [40]. 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.

Barranca del Muerto No. The concentration of phosphorylated sugars increases when the Fosfoenolpiruvzto 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 fosfoenolpiiruvato existing during the night, 0. Data analysis Kinetic data were analyzed by nonlinear regression calculations using a commercial computing program formulated with the algorithm of Marquardt [35]. The kinetic differences between the allosteric activators acquire special relevance under conditions close to those prevailing under illumination, i.

In this loop there are several fsfoenolpiruvato 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 carboxilasaa with an asterisk in Figure 3. Also, because regulation of PEPC activity by metabolite effectors is mostly exerted at subsaturating concentrations of substrate [21], in the studies with the allosteric effectors we used a fixed total PEP tPEP concentration of only 0.


Progressive multiple sequence alignment was carried out with the ClustalX package [38], using penalties based on secondary structure. The results of these kinetic experiments are shown in Figure 1 and summarized in dable 1. It has been propoosed that one fosfoeenolpiruvato 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.

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]. When near physiological concentrations were used, Glc6P was very ineffective in overcoming malate inhibition [14]. Therefore, under our experimental conditions Glc6P is no more effective in counteracting malate inhibition of the amaranth than of the maize enzyme Fig. Sequence alignments and homology model flsfoenolpiruvato.


Neutral amino acids concentrations, particularly that of Gly, increase under photorespiration conditions [15]. Fully expanded leaves were used for the experiments.

Each determination was performed at least in duplicate. 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. Phosphoenolpyruvate carboxylase extraction, purification and assay Plants were kept in darkness for at least 6 h prior carboxklasa extraction. These results show that Gly is not an activator of the dicot enzyme either fosfoebolpiruvato the absence or in the presence of the inhibitor malate.

Term Bank – carboxilasa – Spanish English Dictionary

fosfoenoliruvato Citrate release and activity of phosphoenolpyruvate carboxylase in roots of white lupin in response to varying phosphorus supply. Kinetic data were analyzed by nonlinear regression calculations using a commercial computing program formulated with the algorithm of Marquardt [35].

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. The bicarbonate concentration in an assay medium in contact with air at pH 7.

When the concentration of inhibitor was varied at constant concentration of substrates, the carboxllasa data were fitted to equation 3: 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.


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 [16]. Phosphoenolpyruvate carboxylase assay and kinetic studies. All other chemicals of analytical grade were from standard suppliers.

In the homology models of both enzymes, these parts are forming loops, as expected. No exogenous bicarbonate was added to the assay carboxlasa, so that the concentration of bicarbonate was 0. The activation by Glc6P may, however, play an important role increasing the flux of the C4 cycle at the onset of the light conditions, as mentioned above.

Of particular interest to us is the loop analyzed in the sequence alignments of Figure 3. 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.

Both types of isoenzymes also carboxulasa in their affinity for the substrate PEP, the activator Glc6P and the inhibitor malate. Amaranth Amaranthus hypochondriacus L.

The neutral amino acid binding site is not yet known because no structure with this kind of ligand has been determined so far. The reaction was started by addition of the enzyme preparation.

The standard assay medium, final volume of 0. These results indicate that the binding of malate and that of Glc6P to the amaranth enzyme are competitive. This is consistent with a lack of effect of malate on the binding of Glc6P and, reciprocally, a lack of effect of Glc6P on the binding of malate. Plant material Plants of maize Zea mays L. Protein was measured by the method of Bradford [33], using bovine serum albumin as the standard.

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