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):||25 March 2004|
|PDF File Size:||12.79 Mb|
|ePub File Size:||17.14 Mb|
|Price:||Free* [*Free Regsitration Required]|
These results indicate that the binding of malate and that of Glc6P to the amaranth enzyme are competitive. Progressive multiple sequence alignment was carried out with the ClustalX package , using penalties based on secondary structure. This is consistent with competition between inhibitor and activator for their fosfoenolpriuvato to the enzyme. Phosphoenolpyruvate carboxylase assay and kinetic studies. Citrate release and activity of phosphoenolpyruvate carboxylase in roots of fosfoeonlpiruvato lupin in response to varying phosphorus supply.
A rigid docking of glycine in this position not shown suggested the feasibility of binding of the activator to these residues, as we propose. 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 carboxlasa lpyruvate carboxylase orthophosphate: Plants were kept in darkness for at least 6 h prior to extraction.
The overall identity among monocot cafboxilasa ranged from 80 to carboxulasa The models were validated using ProCheck .
The kinetic differences between the allosteric activators acquire special relevance under fosfoenllpiruvato close to those prevailing under illumination, i. The bicarbonate concentration in an assay medium in contact with air at pH 7.
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.
When the concentration of inhibitor was varied at constant concentration of substrates, the experimental data were fitted to equation 3: 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.
Barranca del Muerto No. The reaction was started by addition of the enzyme preparation.
Plant material Plants of maize Zea mays L. 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: 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.
Of particular interest to us is the loop analyzed in the sequence alignments of Figure 3. 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 .
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. Therefore, under our experimental conditions Glc6P is no more effective in counteracting malate inhibition of the amaranth than of the maize enzyme Fig. 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 .
Nature, In the homology models of both enzymes, these parts are forming loops, as expected. The same solution was always obtained after repeated submissions of the data to this server.
Amaranth Amaranthus hypochondriacus L. Rates in the absence of PEP were negligible. Phosphoenolpyruvate carboxylase extraction, purification and assay. The points in the figures are the experimentally determined values, whereas the curves are calculated from fits of these data to the appropriate equation.
Plants of maize Zea mays L. All the contents of this journal, except where otherwise noted, is licensed under a Flsfoenolpiruvato Commons Attribution License.
Six of these sequences are from monocot plants and the other seven from dicot plants. Sequence alignments and homology model building. 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 Fostoenolpiruvato, or to increase the supply of CO 2 to the bundle sheath cells to prevent photorespiration, in the case of Gly.
The concentration of phosphorylated sugars increases when the Calvin cycle is active.
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 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].
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 results of these kinetic experiments are shown in Figure 1 and summarized in dable 1. Once the levels of malate are high, saturation of the Glc6P allosteric site would give only a marginal advantage.
Term Bank – carboxilasa – Spanish English Dictionary
Accepted June 8, Each determination was performed at least in duplicate. 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 carbkxilasa than those exhibited by the monocot isoenzymes. EDTA ethylenediaminetetraacetic acid disodium salt was from Merck. Phosphoenolpyruvate carboxylase extraction, purification and assay Plants were kept in darkness for at least 6 h prior to fosfoneolpiruvato.
Received February 23,