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 carboxilasaa in soil at five P treatments with P added to obtain shoot P ranging from deficient to adequate varied from 0. We display the results of the kinetics of saturation of the enzyme by its substrate PEP by considering tPEP as the variable carbkxilasa, instead of MgPEP, to facilitate the evaluation of the data in the physiological range of concentration of this metabolite.
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. Activation by Gly helps in increasing the flux through the C4 pathway by effectively counteracting the inhibitory effects of malate, fosoenolpiruvato, therefore, it helps in carblxilasa the concentrations of CO2 in the bundle sheet cells thus overcoming photorespiration.
Six of these sequences are from monocot plants and the other seven from dicot plants. This is consistent with competition between inhibitor and activator for their binding to the enzyme. 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 carboxioasa absence of the inhibitor . When the concentration of inhibitor was varied at constant concentration of substrates, the experimental data were fitted to equation 3: Plants of maize Zea mays L.
Progressive multiple sequence alignment was carried out with the ClustalX package , using penalties based on secondary structure. Although the S 0. Plants were kept in darkness for at least 6 h prior to extraction.
Nishikido, T; Takanashi, H. Phosphoenolpyruvate carboxylase assay and kinetic studies. A rigid docking of glycine in this position not shown suggested the feasibility of binding of the activator to these residues, as we propose.
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.
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. 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: 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.
Rates in the absence of PEP were negligible. 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.
These results indicate that the binding of malate and that of Glc6P to the amaranth enzyme are competitive. Carbodilasa kinetic differences between the carboxillasa activators acquire special relevance under conditions close to those prevailing under illumination, i. Received February 23, These findings suggest that the binding of Glc6P is not affected by the binding of the inhibitor to this enzyme. 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.
Protein was measured by the method of Bradford , using bovine serum albumin as the standard.
FosfoenolPiruvato by Ariadne Heredia on Prezi
Darboxilasa results of these kinetic experiments are shown in Figure 1 and summarized in dable 1. The models were validated using ProCheck .
Phosphoenolpyruvate carboxylase extraction, purification and assay Plants were kept in darkness for at least 6 h prior to extraction. 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].
Neutral amino acids concentrations, particularly that of Gly, increase under photorespiration conditions . Initial velocity data depending upon varied concentration of substrate were fitted to a Hill equation equation 1: Both types of isoenzymes also differ in their affinity for the substrate Fosfoenolpiryvato, the activator Glc6P and the inhibitor malate. These results show that Gly is not an activator of the dicot enzyme carboxxilasa in the absence or in the presence of the inhibitor malate.
Nature, In the experiments in which the concentration of the activator was varied at constant concentration of substrates, equation 2 was used: 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.
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 . Citrate release and activity of phosphoenolpyruvate carboxylase in roots of white lupin in response to varying phosphorus supply. The bicarbonate concentration in an assay medium in contact with air at pH 7. In a broad range of P concentrations in nutrient solutions with P added to obtain shoot P ranging from deficient to near toxicitythe enzyme activity and citrate release were reduced to almost undetectable levels when shoot P was increased to 0.
Phosphoenolpyruvate carboxylase extraction, purification and assay.