The Ionic Strength Changes the Quaternary Structure of Phosphoenolpyruvate Carboxylase from Maize Leaves (original) (raw)
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Maize Phosphoenolpyruvate Carboxylase
Journal of Biological Chemistry, 2005
Phosphoenolpyruvate carboxylases (PEPC, EC 4.1.1.31) from higher plants are regulated by both allosteric effects and reversible phosphorylation. Previous x-ray crystallographic analysis of Zea mays PEPC has revealed a binding site for sulfate ion, speculated to be the site for an allosteric activator,
European Journal of Biochemistry, 1987
Phosphoenolpyruvate carboxylase from maize leaves dissociated into dimers and/or monomers when exposed to increasing ionic strength (e. g. 200 -400 mM NaC1) as indicated by gel filtration experiments. Changes in the oligomerization state were dependent on pH, time of preincubation with salt and protein concentration. A dissociation into dimers and monomers was observed at pH 8, while at pH 7 dissociation into the dimeric form only was observed. Exposure of the enzyme to higher ionic strength decreased the activity in a time-dependent manner. Turnover conditions and glucose 6-phosphate protected the carboxylase from the decay in activity, which was faster at pH 7 than at pH 8. The results suggest that changes in activity of the enzyme, following exposure to high ionic strength, are the consequence of dissociation. Tetrameric and dimeric forms of the phosphoenolpyruvate carboxylase seemingly reveal different catalytic properties. We suggest that the distinct catalytic properties of the different oligomeric species of phosphoenolpyruvate carboxylase and changes in the equilibrium between them could be the molecular basis for an effective regulation of metabolite levels by this key enzyme of C4 plants.
Stability Studies on Maize Leaf Phosphoenolpyruvate Carboxylase: The Effect of Salts
Biochemistry, 1995
The solution stability of phosphoenolpyruvate carboxylase (PEPC) has been determined in the presence of various salts by temperature-accelerated enzyme inactivation and also by using highperformance size-exclusion chromatography. Kosmotropic (water structuring) anions in the Hofmeister series (HP042-, citrate3-, S042-, F-, OAc-) and glutamate stabilized the enzyme most effectively, while C1-(a borderline Hofmeister anion) and Br-(a chaotropic anion) were destabilizing. The effects of the cations on PEPC stability ranged from relatively inert (Na+, K+) to destabilizing ((CH&.N+, N&+, Li+).
Artifacts in the assay of maize leaf phosphoenolpyruvate carboxylase activity due to its instability
Photosynthesis Research, 1988
When the assay of maize leaf phosphoenolpyruvate carboxylase (EC 4.1.1.31) activity is started with phosphoenolpyruvate, much lower reaction rates are obtained as compared to the enzyme-initiated reaction. The difference is due to the lability of the dilute enzyme in the absence of its substrate and is increased with incubation time in the absence of substrate or stabilizers. The activation of the enzyme by glucose-6-phosphate is overestimated with the substrate-initiated assay since a part of the apparent activation is due to stabilization of the enzymic activity by this effector during the minus-substrate preincubation. In contrast, the inhibitory effect ofmalate is underestimated when the reaction is started with the substrate. The enzyme-initiated assay is recommended provided that the necessary corrections for apparent activity in the absence of substrate and for inactivation during the assay at low substrate levels are made.
PLANT PHYSIOLOGY, 1989
Maize (Zea mays L.) leaf phosphoenolpyruvate (PEP) carboxylase activity at subsaturating levels of PEP was increased by the inclusion of glycerol (20%, v/v) in the assay medium. The extent of activation was dependent on H+ concentration, being more marked at pH 7 (with activities 100% higher than in aqueous medium) than at pH 8 (20% activation). The determination of the substrate concentration necessary to achieve half-maximal enzyme activity (So.5) (PEP) and maximal velocity (V) between pH 6.9 and 8.2 showed a uniform decrease in So.5 in the presence of www.plant.org on April 15, 2016 -Published by www.plantphysiol.org Downloaded from