Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.11 (AMPK)
 12,425 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The influence of pH on the in vitro activity and regulatory properties of Sorghum leaf C4 phosphoenolpyruvate carboxylase (PEPC) was investigated with respect to the phosphorylation status of the enzyme. In vitro protein phosphorylation was achieved using the catalytic subunit of a cAMP-dependent protein kinase (PKA) and a recombinant, immunopurified PEPC (0.9 mol of covalent Pi/mol PEPC subunit). Between pH 6.8 and 8, velocity and IC50 for L-malate increased for both the nonphosphorylated and the phosphorylated forms. With respect to the nonphosphorylated PEPC, the phospho-PEPC always gave high values for these kinetic parameters at the pH range investigated, especially between pH 7 and 7.3. The phosphorylation-induced stimulation of PEPC activity was four- to fivefold at pH 7.1 and approximately twofold at pH 7.3. The IC50 for L-malate showed a two- to threefold increase at pH 7.3, but varied less at pH 7.1 upon PEPC phosphorylation. Thus, phosphorylation of PEPC caused a predominant V effect or a mixed (V/IC50) effect at pH 7.1 or 7.3, respectively. This was also observed with the enzyme from desalted crude protein extracts from dark or light-adapted Sorghum leaves and leaf-derived mesophyll protoplasts illuminated in the presence of methylamine, a compound known to increase cytosolic pH (pHc). At pH 7.3, desensitization to L-malate of phospho-PEPC was due to an enhanced ability of PEP to compete with the inhibitor. The positive effector glucose-6P acted similarly to phosphorylation; however, a combination of both factors (glucose-6P and phosphorylation) led to a much larger increase in the IC50 for L-malate than that observed by a single factor.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The effect of pH on the covalent and metabolic control of C4 phosphoenolpyruvate carboxylase from Sorghum leaf. 798 87

Following in situ renaturation and assay of protein kinase activity after denaturing electrophoresis of relatively impure samples of maize phosphoenolpyruvate carboxylase (PEPC) kinase, a approximately 30-kDa polypeptide was implicated as the best candidate for the PEPC kinase catalytic subunit. This kinase's apparent native molecular weight was estimated at 28,000 by gel filtration on a calibrated Superose 12 column (HR 10/30), suggesting that the isolated PEPC kinase is monomeric. This protein-serine kinase was partially purified about 4000-fold from illuminated maize leaves by ammonium sulfate precipitation and sequential chromatography on Ultrogel AcA 54, hydroxylapatite, blue dextran-agarose, and an analytical AcA 54 column. Analysis by denaturing electrophoresis revealed that a 30-kDa polypeptide copurified with PEPC kinase activity during the final step. This highly purified kinase had an apparent Km (PEPC subunit) of 2.5 microM and a Km (total ATP) of 40 microM at pH 8.0, its pH optimum. Upon in vitro phosphorylation of darkform (dephospho) C4 PEPC at Ser-15 (maize PEPC) or Ser-8 (sorghum), the malate sensitivity of the target enzyme decreased significantly. The maize PEPC kinase activity was markedly inhibited by L-malate, a negative allosteric effector of its protein substrate, in a concentration- and pH-dependent manner. Comparative phosphorylation studies with the catalytic subunit of mammalian cAMP-dependent protein kinase and casein revealed that a significant part of the malate inhibition of PEPC kinase activity in vitro was due to this effector's interaction with PEPC. The activity of both the highly purified PEPC kinase and a less pure sample prepared rapidly in the presence of various protease inhibitors was insensitive to Ca2+ chelation or addition. It is concluded that the approximately 30-kDa maize PEPC kinase is a low abundance, Ca(2+)-independent protein-serine kinase that activates its target enzyme by the exclusive phosphorylation of the regulatory serine residue near the N terminus and the resulting decrease in feedback inhibition by L-malate.
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PMID:Partial purification and characterization of phosphoenolpyruvate carboxylase protein-serine kinase from illuminated maize leaves. 834 24

A full-length cDNA for maize root-form phosphoenolpyruvate carboxylase (PEPC) was isolated. In the coding region, the root-form PEPC showed 76 and 77% identity with the C4- and C3-form PEPCs of maize, respectively, at the nucleotide level. At the amino acid level, the root-form was 81 and 85% identical to the C4- and C3-form PEPCs, respectively. The entire coding region was inserted into a pET32a expression vector so that it was expressed under the control of T7 promoter. The purified recombinant root-form PEPC had a Vmax value of about 28 mumol min-1 (mg protein)-1 at pH 8.0. The K(m) values of root-form PEPC for PEP and Mg2+ were one-tenth or less of those of C4-form PEPC when assayed at either pH 7.3 or 8.0, while the value for HCO3- was about one-half of that of C4-form PEPC at pH 8.0. Glucose 6-phosphate and glycine had little effect on the root-form PEPC at pH 7.3; they caused two-fold activation of the C4-form PEPC. The Ki (L-malate) values at pH 7.3 were 0.12 and 0.43 mM for the root- and C4-form PEPCs, respectively. Comparison of hydropathy profiles among the maize PEPC isoforms suggested that several stretches of amino acid sequences may contribute in some way to their characteristic kinetic properties. The root-form PEPC was phosphorylated by both mammalian cAMP-dependent protein kinase and maize leaf protein kinase, and the phosphorylated enzyme was less sensitive to L-malate.
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PMID:Cloning, expression, and characterization of a root-form phosphoenolpyruvate carboxylase from Zea mays: comparison with the C4-form enzyme. 978 61