Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Leishmania mexicana mexicana amastigotes have been shown to contain greater activities than promastigotes of the enzymes that catalyse the beta-oxidation of fatty acids, but lower activities of several glycolytic enzymes, with the activity of pyruvate kinase being especially low. The results suggest the beta-oxidation of fatty acids is relatively more important to Leishmania amastigotes than promastigotes, whereas the reverse is true for glycolysis. Succinic dehydrogenase and peptidase activities were much higher in promastigotes than amastigotes. The activities of glucose-6-phosphatase, fructose-1,6-bisphosphatase, acid phosphatase and glucose-6-phosphate dehydrogenase varied less, although in each case the activity was significantly lower in the mammalian stage. A method for lysing and fractionating L. m. mexicana promastigotes has been developed. Using this procedure it has been established that many of the glycolytic and functionally related enzymes are located in cell organelles, that hexokinase is intimately connected with the particulate part of the parasite, and that the microsomal fraction of L. m. mexicana is very different in composition from the microsomes of mammalian liver cells.
Mol Biochem Parasitol 1982 Mar
PMID:A comparative study of Leishmania mexicana amastigotes and promastigotes. Enzyme activities and subcellular locations. 621 17

Hepatic pyruvate kinase phosphatase activity has been assayed in native conditions, in Sephadex G-25 filtered extracts of rat hepatocytes, by measuring the reactivation rate of glucagon-inactivated pyruvate kinase-L. The ionic requirements for this reaction, as well as the possible regulatory role of some pyruvate kinase ligands, have been investigated. Pyruvate kinase phosphatase activity was dependent on divalent cations (Mg2+, Mn2+ or Co2+). Mg2+ ions highly enhanced the reactivation rate of pyruvate kinase, while the presence of 100 mM KF inhibited this process. Physiological concentrations of phosphoenolpyruvate or fructose 1,6-bisphosphate inhibited pyruvate kinase phosphatase activity. These inhibitory effects were partially antagonized by the presence of L-alanine. Our results suggest that ligands of pyruvate kinase could play a role in the control of pyruvate kinase phosphatase activity(ies), possibly by modifying the conformational state of the substrate protein.
Mol Cell Biochem 1983
PMID:Modulation of pyruvate kinase phosphatase activity in hepatocyte extracts by pyruvate kinase-L ligands. 630 88

We have previously proposed that 2-ketobutyrate is an alarmone in Escherichia coli. Circumstantial evidence suggested that the target of 2-ketobutyrate was the phosphoenol pyruvate: glycose phosphotransferase system (PTS). We demonstrate here that the phosphorylated metabolites of the glycolytic pathway experience a dramatic downshift upon addition of 2-ketobutyrate (or its analogues). In particular, fructose-1,6-diphosphate, glucose-6-phosphate, fructose-6-phosphate and acetyl-CoA concentrations drop by a factor of 10, 3, 4, and 5 respectively. This result is consistent with (i) an inhibition of the PTS by 2-ketobutyrate, (ii) a control of metabolism by fructose-1,6-diphosphate. Since fructose-1,6-diphosphate is an activator of phosphoenol pyruvate carboxylase and of pyruvate kinase, the concentration of their common substrate, phosphoenol pyruvate, does not decrease in parallel.
Mol Gen Genet 1984
PMID:Metabolic alterations mediated by 2-ketobutyrate in Escherichia coli K12. 636 74

In vitro biochemical characteristics of three strains of Haemonchus contortus, benzimidazole-susceptible, mebendazole-resistant and thiabendazole-resistant isolates, were investigated. Steady-state pool sizes of glucose and metabolic intermediates, including adenine nucleotides and end-products revealed no differences between adult worms resistant or susceptible to benzimidazoles in 30-60 min incubations. Possible regulatory steps in the glycolytic pathway are identified as those involving the enzymes hexokinase, phosphofructokinase and pyruvate kinase. The major component of carbohydrate reserves was trehalose, some glycogen was present and the glucose pool was small. On incubation for 18 h in vitro, carbohydrates were metabolised in all three strains. However, in the benzimidazole-susceptible worms there was a preferential use of the glycogen reserves to maintain energy metabolism. All three strains had similar levels of total lipid, total protein and free amino acid and these did not change on incubation. The major products found in the medium on incubation, in vitro, for 18 h were propionate, acetate and propanol, with smaller amounts of ethanol, lactate and malate. All three strains produced a similar sum total of end-products; however, in the mebendazole-resistant strain there appeared to be a diversion of carbon flow to the ethanol-producing pathway. Carbon dioxide production in 60 min incubations was measured using radioactively labelled glucose. A greater output of labelled CO2 was noted under aerobic than anaerobic conditions. This was particularly true of the mebendazole-resistant strain and, in this strain, was sensitive to cyanide. The extent to which metabolic differences noted in the three strains may be related to benzimidazole resistance is not readily apparent.
Mol Biochem Parasitol 1984 Mar
PMID:Energy metabolism of adult Haemonchus contortus in vitro: a comparison of benzimidazole-susceptible and -resistant strains. 642 5

The mechanism of allosteric regulation of rabbit muscle pyruvate kinase (PK) was examined in the presence of the allosteric inhibitor phenylalanine (Phe). Steady-state kinetic, equilibrium binding, and structural studies were conducted to provide a broad data base to establish a reasonable model for the interactions. Phe was shown to induce apparent cooperativity in the steady-state kinetic measurements at pH 7.5 and 23 degrees C. The apparent Km for phosphoenolpyruvate was shown to increase with increasing Phe concentrations. These results imply that Phe reduces the affinity of PK for phosphoenolpyruvate. This conclusion was substantiated by equilibrium binding studies which yielded association constants of phosphoenolpyruvate as a function of Phe concentration. The binding constant of Phe was also determined at pH 7.0 and 23 degrees C. The effect of ligands on the hydrodynamic properties of PK was monitored by difference sedimentation velocity, sedimentation velocity, and equilibrium experiments. The results showed that PK remains tetrameric both in the presence and in the absence of Phe. However, Phe induces a small decrease in the sedimentation coefficient of the enzyme; hence, it suggests a loosening of the protein structure. The accessibility of the sulfhydryl residues of the enzyme also increases in the presence of Phe. Furthermore, the Phe-induced conformational change was approximately 90% complete when only 25% of the binding sites were saturated. This result suggested that the regulatory behavior of PK might satisfactorily be described by the two-state model of Monod-Wyman-Changeux [Monod, J., Wyman, J., & Changeux, J.-P. (1965) J. Mol. Biol. 12, 88-118].
 ...
PMID:Thermodynamic linkages in rabbit muscle pyruvate kinase: kinetic, equilibrium, and structural studies. 648 76

The mechanism of activation by inorganic phosphate and ATP of cardiac muscle pyruvate kinase was studied with the aid of steady-state kinetics. The enzyme was purified to homogeneity to a final specific activity of 400 units/mg (phosphate buffer, pH 7.6, 25 degrees C). At pH 7.6 the enzyme displays Michaelis-Menten kinetics with respect to both its substrates, phosphoenolpyruvate and ADP. Substrate kinetic constants are: app.Km(phosphoenolpyruvate) = 0.04 mM, app.Km(ADP) = 0.22 mM. Under the conditions used in the standard assay the specific activity is greatly enhanced by inorganic phosphate (50 mM) or ATP (2.5 mM). Each of these modifiers, acting separately, increases the Vmax without seriously affecting Michaelis constants and Hill coefficients. In the presence of both Pi and ATP, only a decrease in Vmax was observed. The kinetics of activation by inorganic phosphate of pyruvate kinase was examined. Studying the effect of varying concentrations of Pi on the initial rate we obtained a hyperbolic saturation curve with the app.Km(Pi) = 20 mM and Vmax = 167 units/mg. The evidence is presented that inorganic phosphate is a substrate for a side reaction catalyzed by cardiac pyruvate kinase. It is shown that in the presence of pyruvate, inorganic phosphate and ATP in the assay system, Pi is incorporated into acid-labile products of this reaction, inorganic pyrophosphate being one of them. These findings indicate the existence of an alternative reaction catalyzed by pyruvate kinase by which energy may be stored in the form of inorganic pyrophosphate.
Mol Cell Biochem 1984 Sep
PMID:The influence of inorganic phosphate and ATP on the kinetics of bovine heart muscle pyruvate kinase. 649 21

Glycogen content, glucose consumption and the production of metabolic end products by Calicophoron ijimai were determined under aerobic and anaerobic conditions. The major end products of fermentation were identified as lactic, acetic, propionic, isobutyric and alpha-methylbutyric acids, propionic acid predominating. The activities and properties of some of the enzymes of carbohydrate metabolism were determined. The worms showed high phosphoenolpyruvate carboxykinase, malate dehydrogenase and malate dehydrogenase (decarboxylating) but relatively low pyruvate kinase and very low lactate dehydrogenase activities. The pH optima, coenzyme, cofactor and ionic requirements of the enzymes were similar to those of other helminths. Malate dehydrogenase had an 8-fold greater affinity for oxaloacetate than malate, and was about 14 times more active for oxaloacetate reduction than malate oxidation. Phosphoenolpyruvate carboxykinase was 2.4 times more active and had a 2-fold greater affinity for phosphoenolpyruvate and dinucleotide than pyruvate kinase. The low activities of lactate dehydrogenase and pyruvate kinase but high activities of malate dehydrogenase and phosphoenolpyruvate carboxykinase suggest that anaerobic carbohydrate catabolism follows the fumarate reductase pathway.
Mol Biochem Parasitol 1984 Sep
PMID:Fermentation and the properties of some enzymes of carbohydrate metabolism in the trematode Calicophoron ijimai. 651 86

Glycolytic parameters were determined in recessive yeast mutants with partial defects in carbon catabolite repression. Specific activities of pyruvate kinase and pyruvate decarboxylase in glucose grown cells of all mutant and wild type strains were 4--5 times higher than in ethanol grown cells. Mutants of gene HEX1 had a reduced hexose phosphorylating activity on all media whereas those of gene HEX2 had elevated levels but only in glucose grown cells. Mutants of gene CAT80 were normal in this respect. All other glycolytic enzymes were normal in all mutants. This was also true for glycolytic intermediates. Only hex1-mutants showed a reduced fermentation of repressing sugars. The three genes appear to be involved in catabolite repression of several but not of all repressible enzymes. Even though all three types of mutants show a limited overlap in their effects on certain enzymes, they still are distinctly different in their action spectra. Carbon catabolite repression apparently does not depend on the sole accumulation of glycolytic intermediates. The activity of the products of the three genes HEX1, HEX2 and CAT80 are required directly or indirectly for triggering carbon catabolite repression. Even a small segment of carbon catabolite repression is controlled by several genes with regulatory functions indicating that the entire regulatory circuit is highly complex.
Mol Gen Genet 1980 Jan
PMID:Glycolytic enzymes and intermediates in carbon catabolite repression mutants of Saccharomyces cerevisiae. 698 75

Progress curves of the reaction catalysed by pyruvate kinase from Escherichia coli K12, designed to cover the four-dimensional concentration space of phosphoenolpyruvate, ADP, Mg2+ and ATP in the regulatory region, were recorded with the pH-stat method (pH 7.0 and 25 degrees C). Additional initial-rate measurement were performed to assess specific points. Two methods for the evaluation of progress curves were used: fitting the rate law to the rates obtained from the tangents of the progress curves and fitting the integrated rate law directly to the curves. Two models, both extensions of the concerted model given by Monod, Wyman & Changeux [(1965) J. Mol. Biol. 12, 88--118] with four protomers, could be fitted to the data within the experimental error. Model discrimination in favour of one of these models was possible by proper experimental design. In the selected model one conformational state of the enzyme forms the active complex. The active site of a second conformational state forms abortive complexes with Mg2+, causing strong inhibition at high Mg2+ concentrations. In the absence of ligands, most of the enzyme is in a third state that binds ATP at an allosteric site.
 ...
PMID:Analysis of progress curves. Rate law of pyruvate kinase type I from Escherichia coli. 701 16

This mini review is primarily concerned with the monovalent and divalent cation activation of pyruvate kinase. All preparations of pyruvate kinase from vertebrate tissue which have been examined require monovalent cations such as K+ for catalysis. However, several microbial preparations are not activated by monovalent cations. In fact, E. coli synthesize, depending on growth conditions, 2 different forms of the enzyme; one form is not activated while the other is activated by monovalent cations. The monovalent cation was shown by NMR techniques to bind within 4-8 A of the divalent cation activator and apparently plays a direct role in the catalytic process. As with all kinases, pyruvate kinase requires a divalent cation for catalysis. Mg+2 is optimal for the physiological reaction, however, Co+2, Mn+2, and Ni+2 also activate. The divalent cation activation of several non-physiological reactions catalyzed by pyruvate kinase are reviewed. Several lines of evidence suggest that 2 moles of the divalent cation are required in the catalytic event. However, the specific role of both atoms in the catalytic event have not been thoroughly elucidated.
Mol Cell Biochem 1981 Mar 13
PMID:Pyruvate kinase: activation by and catalytic role of the monovalent and divalent cations. 701 12


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>