scholarly journals Maximum activities and effects of fructose bisphosphate on pyruvate kinase from muscles of vertebrates and invertebrates in relation to the control of glycolysis

1978 ◽  
Vol 174 (3) ◽  
pp. 989-998 ◽  
Author(s):  
Victor A. Zammit ◽  
Isidorus Beis ◽  
Eric A. Newsholme
Keyword(s):  
Pyruvate Kinase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Contractile Activity ◽  
Mass Action ◽  
Glycolytic Flux ◽  
Fructose Bisphosphate ◽  
Efficient System ◽  
Hypoxic Conditions ◽  
Sufficient Energy ◽  
Ratio Data

1. Comparison of the maximum activities of pyruvate kinase with those of phosphofructokinase in a large number of muscles from invertebrates and vertebrates indicates that, in general, in any individual muscle, the activity of pyruvate kinase is only severalfold higher than that of phosphofructokinase. This is consistent with the suggestion, based on mass-action ratio data, that the pyruvate kinase reaction is non-equilibrium in muscle. However, the range of activities of pyruvate kinase in these muscles is considerably larger than that of phosphofructokinase. This difference almost disappears if the enzyme activities from muscles that are known to possess an anaerobic ‘succinate pathway’ are excluded. It is suggested that, in these muscles, phosphofructokinase provides glycolytic residues for both pyruvate kinase (i.e. glycolysis) and phosphoenolpyruvate carboxykinase (i.e. the succinate pathway). This is supported by a negative correlation between the activity ratio, pyruvate kinase/phosphofructokinase, and the activities of nucleoside diphosphokinase in these muscles, since high activities of nucleoside diphosphokinase are considered to indicate the presence of the succinate pathway. 2. The effect of fructose bisphosphate on the activities of pyruvate kinase from many different muscles was studied. The stimulatory effect of fructose bisphosphate appears to be lost whenever an efficient system for supply of oxygen to the muscles is developed (e.g. insects, squids, birds and mammals). This suggests that activation of pyruvate kinase is important in the co-ordinated regulation of glycolysis in anaerobic or hypoxic conditions, when the change in glycolytic flux during the transition from rest to activity needs to be large in order to provide sufficient energy for the contractile activity. However, lack of this effect in the anaerobic muscles of the birds and mammals suggests that another metabolic control may exist for avian and mammalian pyruvate kinase in these muscles.

scholarly journals Properties of pyruvate kinase and phosphoenolpyruvate carboxykinase in relation to the direction and regulation of phosphoenolpyruvate metabolism in muscles of the frog and marine invertebrates

1978 ◽  
Vol 174 (3) ◽  
pp. 979-987 ◽  
Author(s):  
Victor A. Zammit ◽  
Eric A. Newsholme
Keyword(s):  
Pyruvate Kinase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Marine Invertebrates ◽  
Adductor Muscle ◽  
Sea Anemone ◽  
Anaerobic Conditions ◽  
Fructose Bisphosphate ◽  
Low Concentrations ◽  
Optimum Ph ◽  
Hill Coefficients

1. The properties of pyruvate kinase and, if present, phosphoenolpyruvate carboxykinase from the muscles of the sea anemone, scallop, oyster, crab, lobster and frog were investigated. 2. In general, the properties of pyruvate kinase from all muscles were similar, except for those of the enzyme from the oyster (adductor muscle); the pH optima were between 7.1 and 7.4, whereas that for oyster was 8.2; fructose bisphosphate lowered the optimum pH of the oyster enzyme from 8.2 to 7.1, but it had no effect on the enzymes from other muscles. Hill coefficients for the effect of the concentration of phosphoenolpyruvate were close to unity in the absence of added alanine for the enzymes from all muscles except oyster adductor muscle; it was 1.5 for this enzyme. Alanine inhibited the enzyme from all muscles except the frog; this inhibition was relieved by fructose bisphosphate. Low concentrations of alanine were very effective with the enzyme from the oyster (50% inhibition was observed at 0.4mm). Fructose bisphosphate activated the enzyme from all muscles, but extremely low concentrations were effective with the oyster enzyme (0.13μm produced 50% activation). 3. In general, the properties of phosphoenolpyruvate carboxykinase from the sea anemone and oyster muscles are similar: the Km values for phosphoenolpyruvate are low (0.10 and 0.13mm); the enzymes require Mn2+ in addition to Mg2+ for activity; and ITP inhibits the enzymes and the inhibition is relieved by alanine. These latter compounds had no effect on enzymes from other muscles. 4. It is suggested that changes in concentrations of fructose bisphosphate, alanine and ITP produce a coordinated mechanism of control of the activities of pyruvate kinase and phosphoenolpyruvate carboxykinase in the sea anemone and oyster muscles, which ensures that phosphoenolpyruvate is converted into oxaloacetate and then into succinate in these muscles under anaerobic conditions. 5. It is suggested that in the muscles of the crab, lobster and frog, phosphoenolpyruvate carboxykinase catalyses the conversion of oxaloacetate into phosphoenolpyruvate. This may be part of a pathway for the oxidation of some amino acids in these muscles.

Glyconeogenesis from lactate in frog striated muscle

1979 ◽  
Vol 237 (5) ◽  
pp. C231-C236 ◽  
Author(s):  
R. J. Connett
Keyword(s):  
Equilibrium Constant ◽  
Pyruvate Kinase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Striated Muscle ◽  
Krebs Cycle ◽  
Mass Action ◽  
Acetate Incorporation ◽  
Krebs Cycle Intermediates ◽  
Frog Sartorius ◽  
Stimulation Of

The rates of 14carbon incorporation into CO2 and glycogen from [U-14C]-lactate and [1-14C]acetate in frog sartorius muscles were compared. The rates of incorporation into CO2 were similar, while the rate of incorporation of lactate into glycogen was more than 200-fold larger than that of acetate incorporation. It is concluded that the pathway of lactate incorporation into glycogen does not involve Krebs cycle intermediates and is extramitochondrial. To test the possibility that the pathway of lactate incorporation involves net reversal of a pyruvate kinase, the changes in phosphoenolpyruvate and pyruvate concentrations during stimulation of lactate incorporation into glycogen were measured. There wer none. The mass action ratio of pyruvate kinase was calculated. This value was two orders of magnitude from the equilibrium constant and it was concluded that reversal of pyruvate kinase was a very unlikely pathway. To test the possibility that a pathway involving the oxaloacetate-to-phosphoenolpyruvate step was involved the muscles were treated with 3-mercaptopicolinate, an inhibitor of phosphoenolpyruvate carboxykinase. The treatment resulted in decreased incorporation of lactate into glycogen.

Carbohydrate metabolism by primary cultures of rabbit proximal tubules

1989 ◽  
Vol 256 (3) ◽  
pp. C532-C539 ◽  
Author(s):  
M. J. Tang ◽  
K. R. Suresh ◽  
R. L. Tannen
Keyword(s):  
Pyruvate Kinase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Cultured Cells ◽  
Primary Cultures ◽  
Lactate Production ◽  
Proximal Tubules ◽  
Glycolytic Metabolism ◽  
Proximal Tubular Cells ◽  
Tubular Cells ◽  
Proximal Tubular

Renal proximal tubular epithelia were used to assess the factors responsible for the induction of glycolysis in cultured cells. Primary cultures of rabbit proximal tubules, which achieved confluency at 6 days, exhibited hormonal responsiveness and brush-border characteristics typical of proximal tubular cells. Beginning at day 4, these cultured cells exhibited increased glycolytic metabolism reflected by enhanced glucose uptake and lactate production, along with parallel increases in activity of the glycolytic enzymes, pyruvate kinase and lactate dehydrogenase. The gluconeogenic enzymes, phosphoenolpyruvate carboxykinase (PEPCK) and fructose-1,6-bisphosphatase (FDP), were downregulated, and the cultured cells exhibited lower oxygen consumption rates than fresh tubules. Cells grown on a rocker, to mitigate hypoxia, exhibited a metabolic and enzymatic profile similar to cells grown under still conditions. ATP levels in cultured cells were higher than in fresh tubules. Furthermore, pyruvate kinase activity was higher in cells grown in media containing 0.5 as contrasted with 25 mM glucose. The enhanced glycolytic metabolism exhibited by cultured proximal tubular cells appears to be a characteristic of proliferation and is not a response to hypoxia, the Pasteur effect, or environmental glucose.

Control of glycolysis in contracting skeletal muscle. II. Turning it off

2002 ◽  
Vol 282 (1) ◽  
pp. E74-E79 ◽  
Author(s):  
Gregory J. Crowther ◽  
William F. Kemper ◽  
Michael F. Carey ◽  
Kevin E. Conley
Keyword(s):  
Muscle Activation ◽  
Contractile Activity ◽  
Glycolytic Pathway ◽  
Glycolytic Flux ◽  
Resonance Spectroscopy ◽  
Atp Production ◽  
Pressure Cuff ◽  
Muscle Ph ◽  
Glycogen Breakdown ◽  
Hexose Phosphates

Glycolytic flux in muscle declines rapidly after exercise stops, indicating that muscle activation is a key controller of glycolysis. The mechanism underlying this control could be 1) a Ca2+-mediated modulation of glycogenolysis, which supplies substrate (hexose phosphates, HP) to the glycolytic pathway, or 2) a direct effect on glycolytic enzymes. To distinguish between these possibilities, HP levels were raised by voluntary 1-Hz exercise, and glycolytic flux was measured after the exercise ceased. Glycolytic H+ and ATP production were quantified from changes in muscle pH, phosphocreatine concentration, and Pi concentration as measured by 31P magnetic resonance spectroscopy. Substrate (HP) and metabolite (Pi, ADP, and AMP) levels remained high when exercise stopped because of the occlusion of blood flow with a pressure cuff. Glycolytic flux declined to basal levels within ∼20 s of the end of exercise despite elevated levels of HP and metabolites. Therefore, this flux does not subside because of insufficient HP substrate; rather, glycolysis is controlled independently of glycogenolytic HP production. We conclude that the inactivation of glycolysis after exercise reflects the cessation of contractile activity and is mediated within the glycolytic pathway rather than via the control of glycogen breakdown.

Regulation of phosphoenolpyruvate carboxykinase and pyruvate kinase in Saccharomyces cerevisiae grown in the presence of glycolytic and gluconeogenic carbon sources and the role of mitochondrial function on gluconeogenesis

1986 ◽  
Vol 32 (12) ◽  
pp. 969-972 ◽  
Author(s):  
Albert J. Wilson ◽  
J. K. Bhattacharjee
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Pyruvate Kinase ◽  
Growth Medium ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Carbon Sources ◽  
Absolute Requirement ◽  
Fructose 1,6 Bisphosphatase ◽  
Futile Cycling ◽  
Respiratory Deficient

Phosphoenolpyruvate carboxykinase (PEPCKase) and pyruvate kinase (PKase) were measured in Saccharomyces cerevisiae grown in the presence of glycolytic and gluconeogenic carbon sources. The PEPCKase activity was highest in ethanol-grown cells. However, high PEPCKase activity was also observed in cells grown in 1% glucose, especially as compared with the activity of sucrose-, maltose-, or galactose-grown cells. Activity was first detected after 12 h when glucose was exhausted from the growth medium. The PKase activity was very high in glucose-grown cells; considerable activity was also present in ethanol- and pyruvate-grown cells. The absolute requirement of respiration for gluconeogenesis was demonstrated by the absence or significantly low levels of PEPCKase and fructose-1,6-bisphosphatase activities observed in respiratory deficient mutants, as well as in wild-type S. cerevisiae cells grown in the presence of glucose and antimycin A or chloramphenicol. Obligate glycolytic and gluconeogenic enzymes were present sumultaneously only in stationary phase cells, but not in exponential phase cells; hence futile cycling could not occur in log phase cells regardless of the presence of carbon source in the growth medium.

The Role of Insulin in the Regulation of PEPCK and Gluconeogenesis In Vivo

2009 ◽  
Vol 05 (01) ◽  
pp. 34 ◽  
Author(s):  
Christopher J Ramnanan ◽  
Dale S Edgerton ◽  
Alan D Cherrington ◽  
◽  
◽  
...  
Keyword(s):  
Messenger Rna ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Hepatic Glucose Production ◽  
Glycogen Synthesis ◽  
Glucose Production ◽  
Regulatory Control ◽  
Glycolytic Flux ◽  
Large Animals

The regulation of gluconeogenesis by insulin is complex and can involve insulin-mediated events in the liver, as well as in several non-hepatic tissues. Given the complexity of this regulation, it is no surprise that there is considerable debate regarding insulin’s ability to regulate the rate of gluconeogenic formation of glucose-6-phosphate (GNG flux to G6P)in vivo. Conventional ‘textbook’ teaching (based onin vitrostudies of rat liver) depicts that insulin can inhibit this pathway by suppressing the transcription of the enzyme phosphoenolpyruvate carboxykinase (PEPCK). PEPCK is widely considered to be a ‘rate-limiting’ enzyme with high control strength. Additionally, recent data in rodents have led to the conclusion that hyperinsulinemia in the brain can inhibit GNG flux to G6P, likely through transcriptional regulation of PEPCK. Recent data from the authors’ lab have confirmed that the molecular regulation of PEPCK messenger RNA (mRNA) and protein by insulin is conserved in large animals. Acute physiological hyperinsulinemia does not alter gluconeogenic formation of G6P, however, despite substantial reductions in PEPCK protein. This indicates that PEPCK has poor regulatory control over the pathwayin vivo. A physiological rise in insulin suppresses hepatic glucose production by inhibiting glycogenolysis and promoting glycogen synthesis, stimulating glycolytic flux, and redirecting gluconeogenically derived carbon to glycogen. This review documents the relevant ways in which insulin can regulate GNG flux to G6Pin vivo.

In vivo effect of Trigonella foenum graecum on the expression of pyruvate kinase, phosphoenolpyruvate carboxykinase, and distribution of glucose transporter (GLUT4) in alloxan-diabetic rats

2006 ◽  
Vol 84 (6) ◽  
pp. 647-654 ◽  
Author(s):  
Sameer Mohammad ◽  
Asia Taha ◽  
Kamal Akhtar ◽  
R.N.K. Bamezai ◽  
Najma Zaheer Baquer
Keyword(s):  
Skeletal Muscle ◽  
Pyruvate Kinase ◽  
Plasma Glucose ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Glucose Transporter ◽  
Diabetic Rats ◽  
Altered Expression ◽  
Glucose Levels ◽  
Glucose Transporter Glut4

Plasma glucose levels are maintained by a precise balance between glucose production and its use. Liver pyruvate kinase (PK) and phosphoenolpyruvate carboxykinase (PEPCK), 2 key enzymes of glycolysis and gluconeogenesis, respectively, play a crucial role in this glucose homeostasis along with skeletal muscle glucose transporter (GLUT4). In the diabetic state, this balance is disturbed owing to the absence of insulin, the principal factor controlling this regulation. In the present study, alloxan-diabetic animals having high glucose levels of more than 300 mmol/L have been taken and the administration of Trigonella seed powder (TSP) to the diabetic animals was assessed for its effect on the expression of PK and PEPCK in liver and GLUT4 distribution in skeletal muscle of alloxan-diabetic rats. TSP treatment to the diabetic animals resulted in a marked decrease in the plasma glucose levels. Trigonella treatment partially restored the altered expression of PK and PEPCK. TSP treatment also corrected the alterations in the distribution of GLUT4 in the skeletal muscle.

The distribution of calcium in hypoxic cat hearts: the effect of β1-blockade

1978 ◽  
Vol 56 (4) ◽  
pp. 564-570 ◽  
Author(s):  
Cathy C. Y. Pang ◽  
Leslie E. Bailey
Keyword(s):  
Contractile Activity ◽  
Blocking Agent ◽  
Contractile Force ◽  
Rapid Decrease ◽  
Coupling Mechanism ◽  
Hypoxic Conditions ◽  
Concomitant Reduction ◽  
Mammalian Myocardium ◽  
Residual Tissue

Contractile activity decays rapidly during the first few minutes of hypoxia in the mammalian myocardium. These changes may be the result of redistribution of the Ca involved in the excitation–contraction (E–C) coupling mechanism. It was the purpose of this study to determine if distortions in the Ca pool(s) involved in E–C coupling are responsible for the acute reduction in contractile force in the heart. Working, Langendorff kitten heart preparations were perfused with a Krebs–Henseleit solution equilibrated with 5% O2, 5% CO2, and 90% N2. Within 3 min of initiation of this treatment the Ca content of a pool directly involved in E–C coupling (Ca2) was reduced by approximately one-half, and this was accompanied by an equivalent increase in a slowly exchanging Ca pool (Ca3). A concomitant reduction in contractile force was associated with this redistribution of Ca. The Ca remaining in the heart after contractility had been abolished by Ca-free perfusion (residual tissue Ca) was significantly elevated by hypoxia. The β1 blocking agent practolol (10−5 M), prevented the hypoxia-induced reduction in Ca content of Ca2 produced by hypoxia, but had no effect on contractility under hypoxic conditions or during re-oxygenation. Practolol did not prevent the increase in residual tissue Ca induced by hypoxia. It was concluded that the immediate reduction in contractility caused by hypoxia was not causally related to the reduction in the quantity of Ca in Ca2, the pool involved in E–C coupling, but may be related to a rapid decrease in the supply of energy for contraction.

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