Showing papers on "Pyruvate kinase published in 1992"

Double role for pyruvate kinase type M2 in the expansion of phosphometabolite pools found in tumor cells.

Abstract: As a common characteristic of tumor cells, as well as of normal proliferating cells in the G1-phase of cell cycle, one finds constitutive high levels of all the glycolytic metabolites arising between glucose 6-phosphate and phosphoenolpyruvate. Thus, it is that the phosphometabolites fructose 1,6-bisphosphate, ribose 5-P, P-ribose-PP, NAD, GTP, CTO, UTP, UDP-glucose, glycerol 3-P, glycerol phosphocholine and glycerol phosphoethanolamine are useful in the 31P-nuclear magnetic resonance (NMR) detection of solid tumors in animals and man. This expansion of phosphometabolites is achieved during tumor formation as a result of reductions in levels of enzymes degrading phosphometabolites, owing to the decline in the glycerol 3-P hydrogen shuttle, and as a consequence of alterations in the glycolytic isoenzyme equipment. Tumor cells typically express a particular isoenzyme of pyruvate kinase called type M2 (K) at high levels. This isoenzyme is subject to a complex regulation by amino acids, by fructose 1,6-bisphosphate, and by hormonal- and oncogene-dependent phosphorylation. Pyruvate kinase type M2 is a substrate for the oncogene encoded PP60v-src-tyrosine kinase. A drastic decrease in the affinity for its substrate phosphoenolpyruvate found after transformation by the src-oncogene can be explained as a consequence of the phosphorylation of pyruvate kinase in serine and tyrosine. These phosphorylations induce the breakdown of tetrameric pyruvate kinase to the trimeric and dimeric forms. Unlike the tetrameric form, the dimeric form as a low affinity for phosphoenolpyruvate. Partial inactivation of pyruvate kinase and enolase on the one hand, and a hyperactivation of hexokinase and phosphofructokinase on the other hand, lead to an expansion of all metabolites. Only when these metabolites attain high levels, thereby assuring a sufficient supply of metabolites for RNA, DNA, lipid, and complex carbohydrate synthesis, can cell proliferation proceed. This accumulation of metabolites in the G1-phase cells has been termed a "metabolic budget system" because it senses not only the actual nutrient levels, but also the supply over a period of time. Monoclonal antibodies specific for the dimeric form of pyruvate kinase type M2 can be used for the immunohistological detection of tumor cells. The amount of the dimeric form in tumor cells closely correlates with the degree of malignancy and can be used for a nonspecific detection of tumors based on assays performed with patient's plasma.

Cis -regulation of the L-type pyruvate kinase gene promoter by glucose, insulin and cyclic AMP

Abstract: The glucose/insulin response element of the L-pyruvate kinase gene is a perfect palindrome located from nt -168 to -144 with respect to the cap site. This element (L4) is partially homologous to MLTF binding sites. Its full efficiency requires cooperation with a contiguous binding site for HNF4, termed L3 and located from nt -145 to -125. In the presence of the L4 element contiguous to L3, cyclic AMP inhibits activity of the L-PK promoter while in its absence, or when the normal L4-L3 contiguity is modified, cyclic AMP behaves as a transcriptional activator that does not seem to be sequence-specific. Therefore, we propose that the mechanism of inhibition of the L-PK gene by cyclic AMP requires precise interactions between the nucleoprotein complex built up at sites L4 and L3 and other components of the L-PK transcription initiation complex.

Maltose fermentation to acetate, CO2 and H2 in the anaerobic hyperthermophilic archaeon Pyrococcus furiosus: evidence for the operation of a novel sugar fermentation pathway

Abstract: The hyperthermophilic anaerobe Pyrococcus furiosus was grown on maltose as energy and carbon source. During growth 1 mol maltose was fermented to 3–4 mol acetate, 6–7 mol H2 and 3–4 mol CO2. The presence of the following enzyme activities in cell extracts of maltose-grown P. furiosus indicate that the sugar is degraded to pyruvate and H2 by a modified “non-phosphorylated” Entner-Doudoroff-pathway (the values given in brackets are specific enzyme activities at 100 °C): Glucose: methyl viologen oxidoreductase (0.03 U/mg); 2-keto-3-deoxy-gluconate aldolase (0.03 U/mg); glyceraldehyde: benzyl viologen oxidoreductase (2.6 U/mg), glycerate kinase (2-phosphoglycerate forming) (0.48 U/mg), enolase (10.4 U/mg), pyruvate kinase (1.4 U/mg). Hexokinase, glucose-6-phosphate dehydrogenase, 2-keto-3-deoxy-6-phosphogluconate aldolase and phosphofructokinase could not be detected. Further conversion of pyruvate to acetate, CO2 and H2 involves pyruvate: ferredoxin oxidoreductase (0.4 U/mg; T=60°C with Clostridium pasteurianum ferredoxin as electron acceptor), hydrogen: methyl viologen ixodoreductase (3.4 U/mg) and ADP-dependent acetyl-CoA synthetase (1.9 U/mg). Phosphate acetyl transferase and acetate kinase could not be detected. The ADP-dependent acetyl-CoA synthetase catalyzes ATP synthesis via the mechanism of substrate level phosphorylation and apparently constitutes the only ATP conserving site during maltose catabolism in P. furiosus. This novel pathway of maltose fermentation to acetate, CO2 and H2 in the anaerobic archaeon P. furiosus may represent a phylogenetically ancient pathway of sugar fermentation.

Preservation of metabolic activity in lyophilized human erythrocytes.

Abstract: Normal human erythrocytes (RBC) were freeze-dried under conditions that caused minimal modification in normal RBC metabolic activities. Because of the known effects of long-term storage on metabolic activities, we studied the effects of our lyophilization process on RBC metabolism. Of all the metabolic enzymes studied, only triosephosphate isomerase (D-glyceraldehyde-3-phosphate ketol-isomerase, EC 5.3.1.1), enolase (2-phospho-D-glyceratehydro-lyase, EC 4.2.1.11), and pyruvate kinase (ATP:pyruvate O2-phosphotransferase, EC 2.7.1.40) were decreased when compared with fresh control nonlyophilized RBC. The activities of these enzymes did not differ significantly from those of blood bank RBC. Concentrations of high-energy intermediates, ATP, and 2,3-diphosphoglycerate, along with lactate and ATP production were decreased in lyophilized RBC. No enzymes of the pentose phosphate shunt were altered during lyophilization. In addition, our data show that lyophilized RBC possess an intact capacity to (i) synthesize adenine nucleotides and (ii) reduce MetHb to Hb and, thus, maintain the Hb in a functional physiologic state similar to fresh nonlyophilized RBC. The present study demonstrates the possibility of lyophilizing RBC in a manner that maintains normal metabolic and enzymatic function upon rehydration.

Mechanisms of glycolytic control during hibernation in the ground squirrel Spermophilus lateralis

Abstract: The mechanisms of glycolytic rate control during hibernation in the ground squirrel Spermophilus lateralis were investigated in four tissues: heart, liver, kidney, and leg muscle. Overall glycogen phosphorylase activity decreased significantly in liver and kidney to give 50% or 75% of the activity found in the corresponding euthermic organs, respectively. The concentration of fructose-2,6-bisphosphate (F-2,6-P2) decreased significantly in heart and leg muscle during hibernation to 50% and 80% of euthermic tissue concentrations, respectively, but remained constant in liver and kidney. The overall activity of pyruvate dehydrogenase (PDH) in heart and kidney from hibernators was only 4% of the corresponding euthermic values. Measurements of phosphofructokinase (PFK) and pyruvate kinase (PK) kinetic parameters in euthermic and hibernating animals showed that heart and skeletal muscle had typical rabbit skeletal M-type PFK and M1-type PK. Liver and kidney PFK were similar to the L-type enzyme from rabbit liver, whereas liver and kidney PK were similar to the M2 isozyme found primarily in rabbit kidney. The kinetic parameters of PFK and PK from euthermic vs hibernating animals were not statistically different. These data indicate that tissue-specific phosphorylation of glycogen phosphorylase and PDH, as well as changes in the concentration of F-2,6-P2 may be part of a general mechanism to coordinate glycolytic rate reduction in hibernating S. lateralis.

Comparison of endogenous and exogenous sources of ATP in fueling Ca2+ uptake in smooth muscle plasma membrane vesicles.

Abstract: A smooth muscle plasma membrane vesicular fraction (PMV) purified for the (Ca2+/Mg2+)-ATPase has endogenous glycolytic enzyme activity. In the presence of glycolytic substrate (fructose 1,6-diphosphate) and cofactors, PMV produced ATP and lactate and supported calcium uptake. The endogenous glycolytic cascade supports calcium uptake independent of bath [ATP]. A 10-fold dilution of PMV, with the resultant 10-fold dilution of glycolytically produced bath [ATP] did not change glycolytically fueled calcium uptake (nanomoles per milligram protein). Furthermore, the calcium uptake fueled by the endogenous glycolytic cascade persisted in the presence of a hexokinase-based ATP trap which eliminated calcium uptake fueled by exogenously added ATP. Thus, it appears that the endogenous glycolytic cascade fuels calcium uptake in PMV via a membrane-associated pool of ATP and not via an exchange of ATP with the bulk solution. To determine whether ATP produced endogenously was utilized preferentially by the calcium pump, the ATP production rates of the endogenous creatine kinase and pyruvate kinase were matched to that of glycolysis and the calcium uptake fueled by the endogenous sources was compared with that fueled by exogenous ATP added at the same rate. The rate of calcium uptake fueled by endogenous sources of ATP was approximately twice that supported by exogenously added ATP, indicating that the calcium pump preferentially utilizes ATP produced by membrane-bound enzymes.

Normal growth of transgenic tobacco plants in the absence of cytosolic pyruvate kinase.

Abstract: The coding sequence of the cytosolic isozyme of potato tuber pyruvate kinase (PK) was attached to the transit peptide of the small subunit of pea ribulose-1,5-bisphosphate carboxylase oxygenase and placed under the control of the cauliflower mosaic virus 35S promoter. This construct was transformed into Nicotiana tabacum. Unexpectedly, two primary transformants were recovered in which PK activity in leaves was greatly reduced. The reduction in PK activity appeared to result from the complete absence of the cytosolic form of the enzyme (PK(c)). In addition, no PK(c) could be detected on western blots of leaf extracts. Metabolite analyses indicated that the levels of phosphoenolpyruvate are substantially higher in PK(c)-deficient leaves than in wild-type leaves, consistent with a block in glycolysis at the step catalyzed by PK. PK(c) deficiency in the leaves does not appear to adversely affect plant growth. Analysis of progeny indicates that PK(c) deficiency is a heritable trait. The leaves of PK(c)-deficient transformants have normal rates of photosynthetic O(2) evolution and respiratory O(2) consumption, indicating that these plants are using alternative pathways to bypass PK.

Concentrations of D-lactate and its related metabolic intermediates in liver, blood, and muscle of diabetic and starved rats.

Abstract: This is a report investigating the methylglyoxal (MG) bypass in animals, by which D-lactate is produced from triosephosphate via MG. Rats were made diabetic using streptozotocin or starved for 72 h. D-Lactate and various metabolites related to it, such as L-lactate, pyruvate, methylglyoxal, glucose, and inorganic phosphate, were measured in the blood plasma, liver, and skeletal muscle of the rats. Diabetic and starved rats had significantly higher levels of D-lactate in plasma, liver, and skeletal muscle compared with the control group. In contrast, pyruvate levels in plasma, liver, and skeletal muscle was markedly lower than normal in diabetic and starved rats. L-Lactate level lowered markedly in plasma, liver, and skeletal muscle of starved rats and elevated in liver of diabetic rats. Differences between plasma L-lactate level for diabetes and control were not significant. MG level was significantly elevated in plasma and depressed in livers and muscles of starved rats as well as livers of diabetic rats. Hepatic glycerol content was markedly increased in those states. Enzyme activities related to D- and L-lactate, such as pyruvate kinase, phosphofructokinase, aldolase, and glyoxalase I, were measured in the livers of these rats. Pyruvate kinase activity decreased in these states, but other enzyme activities showed no significant changes. D-Lactate was much more excreted than L-lactate in the urine of diabetic and fasted rats compared with normal rats.

Diet-dependent carcinogenesis of pancreatic islets and liver in transgenic mice expressing oncogenes under the control of the L-type pyruvate kinase gene promoter.

Abstract: The liver-type pyruvate kinase (L-PK) gene is controlled positively by insulin and carbohydrates, negatively by glucagon and fasting. Diet-inducible models of carcinogenesis were obtained using the L-PK gene promoter and regulatory sequences to control the expression of c-myc and SV40 T oncogenes in transgenic mice. L-PK/c-myc and L-PK/Tag animals fed a carbohydrate-rich diet developed hepatocarcinomas. In addition, L-PK/Tag animals developed diet-dependent, aggressive endocrine pancreatic tumors, preceded by islet hyperplasia involving the different analysed cell populations (alpha, beta and delta). Expression of the L-PK gene was demonstrated in pancreatic tumors, in rat isolated islets and in rat insulinoma-derived cells (RIN line), revealing a new tissue specificity of the L-PK gene. Our results suggest that this gene may be expressed in islet progenitor cells from which the different mature endocrine cells derive.

Ruminant hepatic metabolism of volatile fatty acids, lactate and pyruvate.

Abstract: Ruminant liver has a quantitatively unique array of substrates presented to it because of the extensive fermentation of dietary carbohydrate to organic acids in the gastrointestinal tract. The single largest input of dietary energy to the extrasplanchnic tissues is acetic acid derived from fermentation, which is largely unused by hepatic parenchyma. The other volatile fatty acids derived from fermentation, primarily propionate, are cleared extensively, but not completely, by the liver. This results in a marked concentration gradient for these acids across the liver lobule. L-lactate, derived from tissue metabolism, as well as variable amounts from rumen fermentation, is used by the liver at a rate lower than for propionate and below the predicted capacity based on in vitro enzymatic and intact cell capacity data. The net result of this selective utilization by the liver results in peripheral blood containing significant concentrations of L-lactate and acetate, but little of the other organic acids. Propionate carbon metabolized by liver cells is converted to glucose with little true loss of carbon, but the same is not true of lactate carbon. The energetic efficiencies by which propionate and lactate carbon are converted to glucose may be much less than optimal because of extensive cycling through pyruvate kinase, pyruvate carboxylase and phosphoenolpyruvate carboxykinase. Inhibition of this futile cycling may represent one avenue by which energetic costs of maintenance and production can be lowered in ruminants.

Elements responsible for hormonal control and tissue specificity of L-type pyruvate kinase gene expression in transgenic mice.

Abstract: L-type pyruvate kinase (L-PK) is a key enzyme of the glycolytic pathway specifically expressed in the liver and, to a lesser degree, in the small intestine and kidney. One important characteristic of L-PK gene expression is its strong activation by glucose and insulin and its complete inhibition by fasting or glucagon treatment. Having previously established that the entire rat L-PK gene plus 3.2 kbp of 5'-flanking region functions in mice in a tissue-specific and hormonally regulated manner, various deletions of these 3.2 kbp of 5'-flanking regions were tested in transgenic animals to map the cis-acting elements involved in transcriptional gene regulation. Our experiments indicate that the proximal region between -183 and +11 confers tissue specificity and contains all the information necessary for dietary and hormonal control of L-PK gene expression in vivo. We found, however, that the transcriptional activity generated by this proximal promoter fragment can be modulated by distal sequences in a tissue-specific manner. (i) Sequences between bp -183 and -392 seem to play a dual role in the liver and small intestine; they induce L-PK expression in the liver but repress it in the small intestine. (ii) Sequences from bp -392 up to -1170 do not seem to have any additional effect on promoter activity. (iii) Between bp -1170 and -2080, we found a putative extinguisher whose transcriptional inhibitory effect is much more marked in the small intestine than in the liver. (iv) Finally, between bp -2080 and -3200, we identified an activating sequence required for full expression of the gene in the liver.

Isolation and characterization of the Aspergillus niger pyruvate kinase gene.

Abstract: The Aspergillus niger gene encoding pyruvate kinase was cloned by heterologous hybridization using a fragment from the corresponding yeast gene as a probe. The primary structure of the gene, including 5′ and 3′ flanking sequences, was determined. The structural part of the A. niger pkiA gene is 2054 bp long and is interupted by seven putative introns. Splicing of the intron sequences results in an open reading frame of 1578 bp, encoding a protein of 526 amino-acid residues and a molecular weight of 58 130 Da. Extensive homology is found with pyruvate kinase from A. nidulans; only 33 amino acids are different between both proteins. Transformation experiments using the pyr A gene as a selection marker and the subcloned pkiA gene as a co-transforming marker led to increased levels of pyruvate kinase. Analysis of the transformants showed that in none of the transformants integration had occurred at the pkiA locus. Predominantly co-integration of the pyrA-and the pkiA-containing plasmids was found in the cases examined.

Study on human erythrocyte thioltransferase: comparative characterization with bovine enzyme and its physiological role under oxidative stress.

Abstract: Thioltransferase, an enzyme which catalyzes the thiol/disulfide exchange reaction in the presence of GSH, was purified to homogeneity on 15% SDS-PAGE from human (36,000-fold purification) and bovine (23,000-fold) erythrocyte hemolysates. These enzymes had similar properties in their monomeric structures (M(r) = 11,000) and broad specificities for substrates ranging from low-molecular disulfides (S-sulfocysteine, cystamine, and cystine) to protein disulfides (trypsin and insulin). They were highly sensitive to SH-reagents (monoiodoacetic acid and mercuric chloride), but were protected from inactivation by the presence of disulfides (GSSG, cystamine, and cystine). Phosphofructokinase and pyruvate kinase that had been inactivated by disulfides were reactivated effectively by the addition of thioltransferase with GSH. In addition, disulfides in membrane proteins of human erythrocytes that have been oxidatively damaged by diamide treatment were reduced to the SH-free form more effectively by incubation with thioltransferase.

Effects of microgravity and tail suspension on enzymes of individual soleus and tibialis anterior fibers.

Abstract: Selected enzymes of energy metabolism were measured in random individual fibers of soleus and tibialis anterior (TA) muscles from rats exposed for 2 wk to spaceflight (F) aboard COSMOS 2044 or tail suspension (T) and from synchronous controls. Average size of soleus fibers (dry weight per unit length) was reduced 37% in F and T fibers; there was little change in TA fibers. Enzyme changes were more pronounced in soleus than in TA fibers. Three enzymes characteristic of fast-twitch muscles, pyruvate kinase, glycerol-3-phosphate dehydrogenase, and 1-phosphofructokinase, were elevated in F and T soleus fibers, but changes in phosphofructokinase were not statistically significant. 3-Ketoacid-CoA transferase, characteristic of slow-twitch muscles, did not change significantly in either F or T fibers. Hexokinase, usually moderately higher in slow- than in fast-twitch muscles, increased markedly in both F and T fibers. In TA fibers analyzed for hexokinase, malate dehydrogenase, phosphohexoisomerase, and pyruvate kinase, only hexokinase and malate dehydrogenase showed significant changes. Hexokinase increased 83% in one of two T muscles. Enzyme data for TA fibers typed by myosin adenosinetriphosphatase were more informative: phosphofructokinase, phosphorylase, and glycerol-3-phosphate dehydrogenase were increased in type IIb fibers of either F or T muscles or both. Malate dehydrogenase was not changed in fibers of any type in either F or T muscle.

Pyruvate-kinase isoenzymes from zygotic and microspore-derived embryos of Brassica napus : Developmental profiles and subunit composition.

Abstract: Polyclonal antibodies against castor-oil seed cytosolic and leucoplastic pyruvate kinases (PKc and PKp, respectively; EC 2.7.1.40) were utilized to examine the subunit compositions and developmental profiles of canola (Brassica napus L. cv. Topas) PKc and PKp over 6 d of seed germination and 35 d of culture of microspore-derived embryos. The PKc from germinating seeds appears to be composed of a single type of 56-kDa subunit, whereas the enzyme from cultured embryos contains equal proportions of immunologically related 57- and 56-kDa subunits. The PKp was immunologically undetectable in germinating seeds, while the enzyme from cultured embryos consisted of immunologically related 64- and 58-kDa subunits in a ratio of about 1∶2, respectively. The large increase in PK activity that occurs between the second and fourth days of seed gemination is based upon de-novo synthesis of PKc. Between 7 and 14 d of culture of microspore-derived embryos, the levels of PKp and PK maximal activity increased approx. 3- and 2.5-fold, respectively. These increases were coincident with an approximately fourfold rise in the in-vivo pyruvate: phosphoenolpyruvate concentration ratio. Conversely, PKc was not only far less abundant relative to PKp, but its level remained constant over 35 d of microspore-embryo culture. Developing non-zygotic (microspore-derived) embryos strongly resembled ripening zygotic (seed) embryos in terms of PK specific activity as well as relative amounts and subunit compositions of PKc and PKp. The results indicate that the synthesis of PK isoenzymes in B. napus seeds is highly regulated and that this regulation follows a preset developmental program.