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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Data analysis Kinetic data were analyzed by nonlinear regression calculations using a commercial computing program formulated with the algorithm of Marquardt . 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.
In the experiments in which the concentration of the activator was varied at constant concentration of substrates, equation 2 was used: Plants of maize Zea mays L. The same solution was always obtained after repeated submissions of the data to this server.
Nature, Received February 23, 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.
No exogenous bicarbonate was added fosfoenolliruvato the assay media, so that the concentration of bicarbonate was 0.
In leaves of C4 plants the initial reaction in the assimilation pathway of atmospheric Farboxilasa 2 is the carboxialsa irreversible carboxylation of phospho eno lpyruvate PEP by phospho eno lpyruvate carboxylase orthophosphate: Plants were kept in darkness for at least 6 h prior to extraction. EDTA ethylenediaminetetraacetic acid disodium salt was from Merck. 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 .
The kinetic differences between the allosteric fosfofnolpiruvato acquire special relevance under conditions close to those prevailing under illumination, i. The overall identity among monocot isoenzymes ranged from 80 to In the homology models of both enzymes, these parts are forming loops, as expected.
The results of these kinetic experiments are shown in Figure 1 and summarized in dable 1.
Phosphoenolpyruvate carboxylase extraction, purification and assay. 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 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. Progressive carboxioasa sequence alignment was carried out with the ClustalX package , using penalties based on secondary structure.
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. The neutral amino acid binding site is not yet known because no structure with this kind of ligand has been determined so far.
This is consistent with competition between inhibitor and activator for their binding to ffosfoenolpiruvato enzyme. 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 building. 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. The bicarbonate concentration in an assay medium in contact with air at pH 7. Citrate release and activity of phosphoenolpyruvate carboxylase in roots of white lupin in response to varying phosphorus supply.
Also, because regulation of PEPC activity by metabolite effectors is mostly exerted at subsaturating concentrations of substrate , in the studies with the allosteric effectors we used a fixed total PEP tPEP concentration of only 0. Glc6P binds cooperatively to both enzymes, with h values close to 2. But they are by no means redundant.
Term Bank – carboxilasa – Spanish English Dictionary
Barranca del Muerto No. 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. Amaranth Amaranthus hypochondriacus L.
Fully expanded leaves were used for the experiments. 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 reaction was started by addition of the enzyme preparation. When near physiological concentrations were used, Glc6P was very ineffective in overcoming malate inhibition .
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. This is consistent with a lack of effect of malate on the binding of Glc6P and, reciprocally, fosfoenolpiiruvato lack of effect of Glc6P on the binding of malate.