+ Site Statistics
+ Search Articles
+ Subscribe to Site Feeds
Most Shared
PDF Full Text
+ PDF Full Text
Request PDF Full Text
+ Follow Us
Follow on Facebook
Follow on Twitter
Follow on LinkedIn

+ Translate
+ Recently Requested

The Interactive Effects of pH, L-Malate, and Glucose-6-Phosphate on Guard-Cell Phosphoenolpyruvate Carboxylase

The Interactive Effects of pH, L-Malate, and Glucose-6-Phosphate on Guard-Cell Phosphoenolpyruvate Carboxylase

Plant Physiology 103(4): 1189-1194

The interactive effects of pH, L-malate, and glucose-6-phosphate (Glc-6-P) on the Vmax and Km of guard-cell (GC) phosphoenolpyruvate (PEP) carboxylase (PEPC) of Vicia faba L. were determined. Leaves of three different physiological states (closed stomata, opening stomata, open stomata) were rapidly frozen and freeze dried. GC pairs dissected from the leaves were individually extracted and individually assayed for the kinetic properties of PEPC. Vmax was 6 to 9 pmol GC pair-1 h-1 and was apparently unaffected to a biologically significant extent by the investigated physiological states of the leaf, pH (7.0 or 8.5), L-malate (0, 5, or 15 mM), and Glc-6-P (0, 0.1, 0.5, 0.7, or 5 mM). As reported earlier, the Km(PEP.Mg) was about 0.2 mM (pH 8.5) or 0.7 mM (pH 7.0), which can be compared with a GC [PEP] of 0.27 mM. In the study reported here, we determined that the in situ GC [Glc-6-P] equals approximately 0.6 to 1.2 mM. When 0.5 mM Glc-6-P was included in the GC PEPC assay mixture, the Km(PEP.Mg) decreased to about 0.1 mM (pH 8.5) or 0.2 mM (pH 7.0). Thus, Glc-6-P at endogenous concentrations would seem both to activate the enzyme and to diminish the dramatic effect of pH on Km(PEP.Mg). Under assay conditions, L-malate is an inhibitor of GC PEPC. In planta, cytoplasmic [L-malate] is approximately 8 mM. Inclusion of 5 mM L-malate increased the Km(PEP.Mg) to about 3.6 mM (pH 7.0) or 0.4 mM (pH 8.5). Glc-6-P (0.5 mM) was sufficient to relieve L-malate inhibition completely at pH 8.5. In contrast, approximately 5 mM Glc-6-P was required to relieve L-malate inhibition at pH 7.0. No biologically significant effect of physiological state of the tissue on GC PEPC Km(PEP.Mg) (regardless of the presence of effectors) was observed. Together, these results are consistent with a model that GC PEPC is regulated by its cytosolic chemical environment and not by posttranslational modification that is detectable at physiological levels of effectors. It is important to note, however, that we did not determine the phosphorylation status of GC PEPC directly or indirectly (by comparison of the concentration of L-malate that causes a 50% inhibition of GC PEPC).

(PDF emailed within 0-6 h: $19.90)

Accession: 009593238

Download citation: RISBibTeXText

PMID: 12232011

DOI: 10.2307/4275523

Related references

Re evaluation of the effects of glucose 6 phosphate and malate on the catalytic properties of phosphoenolpyruvate carboxylase from cynodon dactylon under physiological assay conditions. Australian Journal of Plant Physiology 17(4): 407-412, 1990

Lessened malate inhibition of guard-cell phosphoenolpyruvate carboxylase velocity during stomatal opening. FEBS Letters 352(1): 45-48, 1994

No light activation and high malate sensitivity of phosphoenolpyruvate carboxylase in guard cell protoplasts of commelina communis l. Journal of Experimental Botany 41(230): 1103-1108, 1990

A study of the in-vitro regulation of phosphoenolpyruvate carboxylase from the epidermis of Commelina communis by malate and glucose-6-phosphate. Planta 155(5): 416-422, 1982

Modulation by bicarbonate of catalytic and regulatory properties of C4 phosphoenolpyruvate carboxylase from Amaranthus hypochondriacus: Desensitization to malate and glucose 6-phosphate and sensitization to Mg2+. Plant & Cell Physiology 39(12): 1294-1298, 1998

Effects of sulfite on phosphoenolpyruvate carboxylase and nad phosphate dependent malate dehydrogenase in epidermal peels in two cultivars of pea. Physiologia Plantarum 79(3): 491-496, 1990

Role of malate synthesis mediated by phosphoenolpyruvate carboxylase in guard cells in the regulation of stomatal movement. Plant & Cell Physiology 41(1): 10-15, 2000

Effects of sulfite on phosphoenolpyruvate carboxylase and nicotinamide adenine dinucleotide phosphate-dependent malate dehydrogenase in epidermal peels in two cultivars of pea. Physiologia Plantarum 79: 1-6, 1990

Purification and characterization of phosphoenolpyruvate carboxylase from Brassica napus (rapeseed) suspension cell cultures: implications for phosphoenolpyruvate carboxylase regulation during phosphate starvation, and the integration of glycolysis with nitrogen assimilation. European Journal of Biochemistry 267(14): 4465-4476, 2000

Activation of maize (Zea mays L.) phosphoenolpyruvate carboxylase by glucose-6-phosphate and glycine: effects of pH and Mg2+. Photosynthetica 19(2): 177-182, 1985

Activation of maize zea mays phosphoenolpyruvate carboxylase by glucose 6 phosphate and glycine effects of ph and magnesium. Photosynthetica (Prague) 19(2): 177-182, 1985

Studies on plant phosphoenolpyruvate carboxylase. VI. Stabilizing effect of glucose-6-phosphate and glycine to sorghum leaf PEP carboxylase. Acta Phytophysiologia Sinica 8(1): 9-16, 1982

Kinetic properties of guard-cell phosphoenolpyruvate carboxylase. Biochemie und Physiologie der Pflanzen 186(5-6): 317-325, 1990