Liver Phosphofructokinase Research Articles

Purification and properties of phosphofructokinase 2/fructose 2,6-bisphosphatase from chicken liver and from pigeon muscle.

Phosphofructokinase 2 and fructose 2,6-bisphosphatase extracted from either chicken liver or pigeon muscle co-purified up to homogeneity. The two homogeneous proteins were found to be dimers of relative molecular mass (Mr) close to 110,000 with subunits of Mr 54,000 for the chicken liver enzyme and 53,000 for the pigeon muscle enzyme. The latter also contained a minor constituent of Mr 54,000. Incubation of the chicken liver enzyme with the catalytic subunit of cyclic-AMP-dependent protein kinase in the presence of [gamma-32P]ATP resulted in the incorporation of about 0.8 mol phosphate/mol enzyme. Under similar conditions, the pigeon muscle enzyme was phosphorylated to an extent of only 0.05 mol phosphate/mol enzyme and all the incorporated phosphate was found in the minor 54,000-Mr constituent. The maximal activity of the native avian liver phosphofructokinase 2 was little affected by changes of pH between 6 and 10. Its phosphorylation by cyclic-AMP-dependent protein kinase resulted in a more than 90% inactivation at pH values below 7.5 and in no or little change in activity at pH 10. Intermediary values of inactivation were observed at pH values between 8 and 10. Muscle phosphofructokinase 2 had little activity at pH below 7 and was maximally active at pH 10. Its partial phosphorylation resulted in a further 25% decrease of its already low activity measured at pH 7.1 and in a negligible inactivation at pH 8.5. Phosphoenolpyruvate and citrate inhibited phosphofructokinase 2 from both origins non-competitively. The muscle enzyme and the phosphorylated liver enzyme displayed much more affinity for these inhibitors than the native liver enzyme. Fructose 2,6-bisphosphatase from both sources had about the same specific activity but only the chicken liver enzyme was activated about twofold upon incubation with ATP and cyclic-AMP-dependent protein kinase. All enzyme forms were inhibited by fructose 6-phosphate and this inhibition was released by inorganic phosphate and by glycerol 3-phosphate. Both liver and muscle fructose 2,6-bisphosphatases formed a 32P-labeled enzyme intermediate when incubated in the presence of fructose 2,6-[2-32P]bisphosphate.

Influence of pH on the regulatory kinetics of rat liver phosphofructokinase: a thermodynamic linked-function analysis.

The relationship between pH and the MgATP inhibition of rat liver phosphofructokinase has been quantiatively evaluated by utilization of a thermodynamic linked-function approach. This approach obviates the need to presuppose discrete inhibited and active states of the enzyme. The behavior of the apparent Michaelis constant for fructose 6-phosphate (Fru-6-P) over a 100-fold concentration range of MgATP conforms to the behavior predicted by the linked-function theory in that, a high concentrations of MgATP, saturation of the inhibitory effect is achieved, a result not predicted by a mutually exclusive two-state model. This behavior is described by the relationship Ka = Ka0[(Kix0 + [X])]/(Kix0 + Q[X])], where Ka is the apparent Michaelis constant for Fru-6-P, Ka0 is the Michaelis constant for Fru-6-P in the absence of MgATP, Kix0 is the dissociation constant of MgATP in the absence of Fru-6-P, and Q is the coupling term that quantitatively describes the finite degree of antagonism between MgATP and Fru-6-P. The free energy of interaction between MgATP and Fru-6-P, obtained from Q, is 1.9 kcal/mol at 25 degrees C. Ka0 and Kix0 are 0.17 and 0.3 mM, respectively. The influence of pH on these three parameters was then systematically investigated, and only Ka0 increased substantially with decreasing pH. Consequently, it is concluded that decreasing the pH does not increase the apparent Ka for Fru-6-P by augmenting the binding or inhibition by MgATP to a significant extent but rather by directly affecting the intrinsic affinity of the enzyme for Fru-6-P. The pK for this effect is 8.1.

Phosphate dependency of phosphofructokinase 2.

Experiments performed at micromolar concentrations of inorganic phosphate support the conclusion that liver phosphofructokinase 2 would be completely inactive in the absence of inorganic phosphate or arsenate. The concentration of inorganic phosphate that allowed half-maximal activity decreased with increasing pH, being approximately 0.11 mM at pH 6.5 and 0.05 mM at pH 8. The effect of phosphate was to increase V and to decrease Km for fructose 6-phosphate, without affecting Km for ATP. Citrate and P-enolpyruvate inhibited the enzyme non-competitively with fructose 6-phosphate and independently of the concentration of inorganic phosphate. Phosphorylation of the enzyme by the catalytic subunit of cyclic-AMP-dependent protein kinase did not markedly modify the phosphate requirement and its effect of inactivating phosphofructokinase 2 could not be counteracted by excess phosphate. A nearly complete phosphate dependency was also observed with phosphofructokinase 2 purified from Saccharomyces cerevisiae or from spinach leaves. By contrast, the fructose 2,6-bisphosphatase activity of the liver bifunctional enzyme was not dependent on the presence of inorganic phosphate. Phosphate increased this activity about threefold when measured in the absence of added fructose 6-phosphate and a half-maximal effect was reached at approximately 0.5 mM phosphate. Like glycerol phosphate, phosphate counteracted the inhibition of fructose 2,6-bisphosphatase by fructose 6-phosphate, but a much higher concentration of phosphate than of glycerol phosphate was required to reach this effect.

Modulation of muscle phosphofructokinase at physiological concentration of enzyme.

Two approaches have been used to study the allosteric modulation of phosphofructokinase at physiological concentration of enzyme; a "slow motion" approach based on the use of a very low Mg2+/ATP ratio to conveniently lower Vmax, and the addition of polyethylene glycol as a "crowding" agent to favor aggregation of diluted enzyme. At 0.6 mg/ml muscle phosphofructokinase exhibited a drastic decrease in the ATP inhibition and the concomitant increase in the apparent affinity for fructose-6-P, as compared to a 100-fold diluted enzyme. Similar results were obtained with diluted enzyme in the presence of 10% polyethylene glycol (Mr = 6000). Results with these two approaches in vitro were essentially similar to those previously observed in situ (Aragón, J. J., Felíu, F. E., Frenkel, R., and Sols, A. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 6324-6328), indicating that the enzyme is strongly dependent on homologous interactions at physiological concentrations. With polyethylene glycol it was observed that within the physiological range of concentration of substrates and the other positive effectors, fructose-2,6-P2 still activates the liver phosphofructokinase although it no longer significantly affects the muscle isozyme. In the presence of polyethylene glycol, muscle phosphofructokinase can approach its maximal rate even in the presence of physiologically high concentrations of ATP. Three minor activities of muscle phosphofructokinase have been studied at high enzyme concentration: the hydrolysis of MgATP (ATPase) and fructose-1,6-P2 (FBPase), produced in the absence of the other substrate, and the reverse reaction from MgADP and fructose-1,6-P2. The kinetic study of these activities has allowed a new insight into the mechanisms involved in the modulation of phosphofructokinase activity. The binding of (Mg)ATP at its regulatory site reduces the ability of the enzyme to cleave the bond of the terminal phosphate of MgATP at the substrate site. The positive effectors (Pi, cAMP, NH+4, fructose-1,6-P2, and fructose-2,6-P2) decrease the inhibitory effect of MgATP. Citrate and fructose-2,6-P2 both act as mechanistically "secondary" effectors in the sense that citrate does not inhibit and fructose-2,6-P2 does not activate the FBPase activity, requiring both the presence of ATP to affect the enzyme activity. In conclusion it appears that the regulatory behavior of mammalian phosphofructokinases is utterly dependent on the fact of their high concentrations in vivo.

Purification of rabbit liver phosphofructokinase and its properties under simulatingin vivo conditions

Phosphofructokinase (EC 2.7.1.11) from rabbit liver was purified to homogeneity. Preincubation of enzyme results in nonlinearity of enzyme activity with enzyme concentration. Therefore K0·5 of enzyme for fructose 6 phosphate in the absence or presence of fructose 2,6 bisphosphate or polyethylene glycol or in the presence of both was determined at physiological concentrations of its various effectors by taking the initial rate obtained by adding the enzyme last. They decrease the K0·5 value from 4·1 mM to about 0·2mM. The K0·5 of enzyme for fructose 2,6 bisphosphate was also determined under the above conditions. It is about 4·3 μM. Transient kinetics of phosphofructokinase at varying concentrations of enzyme in the presence of fructose 2,6 bisphosphate or polyethylene glycol or in the presence of both were studied. It was found that although they decrease t1/ 2 i.e. the time to reach half the maximal steady rate by about 5-8 fold, it was about constant at varying concentrations of the enzyme. These results indicate that fructose 2,6 bisphosphate and polyethylene glycol decrease K0·5 of the enzyme for fructose 6 phosphate not by associating the enzyme to higher aggregates, but by a different mechanism.

Quantification of liver and kidney phosphofructokinase by radioimmunoassay in fed, starved and alloxan-diabetic rats.

A newly developed specific radioimmunoassay was used to quantify phosphofructokinase protein directly and independently of assayable activity in liver and kidney cytosol of normal fed, starved and alloxan-diabetic rats. In the fed state, liver phosphofructokinase concentration was 0.096 microM and the kidney enzyme was 0.086 microM (mumol/kg of tissue). In the starved state (24h), liver and kidney phosphofructokinase concentrations decreased by 30%. Prolonged starvation up to 72h did not further decrease enzyme concentration. In liver, total enzyme content during starvation declined by more than 50%, secondary also to a decrease in liver weight. In the alloxan-diabetic rats, there was a 22% decrease in enzyme protein concentration in liver and kidney. Total enzyme content per liver actually decreased much more (46%), because diabetes also resulted in a decrease in liver size. In conjunction with assayable activity measurements, the results of the radioimmunoassay allowed us to calculate the apparent specific activity of the enzyme. The specific activity of the kidney enzyme was 2-3 times that of the liver. Little or no change in specific activity of the liver or kidney enzyme occurred as a result of starvation or chemically induced diabetes. Tissue enzyme concentrations of phosphofructokinase unequivocally reconcile the ultimate results of changing rates of synthesis and degradation and are useful data in the design of spectrophotometric, kinetic, aggregation-disaggregation and other studies.

Properties of the phosphofructokinase regulatory factors

The work presented herein describes many of the physiological properties of the phosphofructokinase regulatory factors. Factor activity can be separated into two discrete fractions, which were designated factor A and factor B, based on their respective charges. A preparation containing both factor A and factor B did not protect the following key carbohydrate-metabolizing enzymes from thermal inactivation: glucokinase, glucose-6-phosphatase (solubilized or nonsolubilized forms), pyruvate kinase, glucose-6-P dehydrogenase, muscle-type phosphofructokinase, or the minor liver phosphofructokinase isozyme. Factor activity in this sample was found to be Pronase sensitive, irreversibly precipitated by trichloroacetic acid, reversibly precipitated by adjusting the sample to a pH of 3.0, and stable to heating at 98 °C for 20 min. Distribution studies indicated that factor activity was found only in the soluble cell fraction and not in the mitochondrial or nuclear fractions. Factor activity was retained by 12,000–14,000 molecular weight cut-off (MWCO) dialysis tubing, and not retained by 50,000 MWCO dialysis tubing. These studies indicate that fructose-2,6-P 2, calmodulin, or insulin-generated mediator are not associated with factor activity. Although fructose-2,6-P 2 did not, both factor preparations protect the major liver phosphofructokinase isozyme (liver PFK) from inactivation by lysosomal extracts. In the diabetic rat, the activities of both factors are greatly reduced but return to near normal levels after 48 h of insulin administration. These data suggest that factor B had little or no effect on the kinetic properties of liver PFK. However, factor A was a K-type activator with respect to fructose-6-P, increasing both the K m and K i for ATP, and slightly increasing the V m .

The effect of glucose on the activity of phosphofructokinase in the mucosa of rat small intestine.

In common with other phosphofructokinase isoenzymes, phosphofructokinase in the epithelial cells of rat small-intestinal mucosa is activated by fructose 2,6-bisphosphate. However, fructose 2,6-bisphosphate was found not to be present in mucosa as judged by three criteria: (1) chromatography on Sephadex G-25 of crude mucosal extracts from fed rats did not result in a decrease, or indeed any change, in the activity of phosphofructokinase under suboptimal conditions at pH7; (2) ultrafiltrates of mucosal extracts did not possess any acid-labile activating activity when tested against chromatographed liver phosphofructokinase; (3) phosphofructokinase-2 activity was not detectable in mucosal extracts. Furthermore, the perfusion in vitro of isolated loops of jejunum or the incubation of mucosal scrapings from either fed rats or rats starved for 48 h showed that the activity of mucosal phosphofructokinase is not subject to short-term regulation by glucose. These observations are consistent with the view that phosphofructokinase is the rate-limiting enzyme of glycolysis in intestinal mucosa and account for the fact that the rate of glucose utilization by rat small intestine is not very responsive to changes in the concentration of glucose in the lumen.

Activation of phosphofructokinase and pyruvate kinase by 6 phosphogluconate in chicken liver (Gallus domesticus): no evidence for a regulatory role.

Phosphofructokinase and pyruvate kinase in crude extracts of chick liver were activated by 6 phosphogluconate at subsaturating concentrations of their respective substrates. The apparent Ka for phosphofructokinase was 0.79 mM and for pyruvate kinase 0.44 mM. Total pentose phosphate dehydrogenase activity was low in the livers of both fed and starved chicks. Hepatic 6 phosphogluconate concentration was too low to be measured accurately by a conventional spectrophotometric method. It is concluded that the concentration of 6 phosphogluconate is too low for it to have a role in the regulation of phosphofructokinase and pyruvate kinase activities in chicken liver.

Regulation of glycolysis in lizards: kinetic studies on liver pyruvate kinase and phosphofructokinase from Lacerta galloti

Kinetic studies were carried out on pyruvate kinase and phosphofructokinase from the lizard Lacerta galloti. Pyruvate kinase is inhibited by ATP and activated by fructose 1,6-biphosphate giving an hyperbolic saturation curve for ATP without the activator which becomes sigmoidal at saturating concentrations of fructose 1,6-biphosphate, giving a moderate cooperativity with a Hill coefficient of h = 1.72. Binding of fructose 1,6-biphosphate to pyruvate kinase was studied as protection effect against thermal denaturation, this being the most suitable ligand tested to avoid the loss of activity. Phosphofructokinase is inhibited by ATP at millimolar range and activated by AMP and by fructose 2,6-biphosphate, AMP being the more efficient activator.

Influence of fructose 2,6-bisphosphate on the aggregation properties of rat liver phosphofructokinase.

The influence that fructose 2,6-bisphosphate (Fru-2,6-BP) has on the aggregation properties of rat liver phosphofructokinase has been studied by observing the fluorescence polarization of the enzyme covalently bound to the fluorescent probe pyrenebutyric acid. Fru-2,6-BP dramatically slows the dissociation of the high molecular weight aggregate forms of the enzyme when the enzyme is diluted to 3.2 micrograms/ml (4 X 10(-8) M subunits). Furthermore, Fru-2,6-BP is a strong promoter of reassociation to tetramer and larger forms if the enzyme has been previously allowed to dissociate to the dimer in its absence. Unlike many other positive effectors of liver phosphofructokinase, Fru-2,6-BP is also able to overcome the tendency of MgATP to promote tetramer formation and instead stabilize a very high degree of high molecular weight aggregate formation even in the presence of MgATP. The apparent affinity of liver phosphofructokinase for Fru-2,6-BP was measured by its ability to promote reassociation and compared to that for Fru-1,6-BP. The apparent dissociation constant for Fru-2,6-BP under these conditions is 36 microM, about 40-fold lower than the value of 1.4 mM measured for Fru-1,6-BP. Both ligands demonstrate synergism with the substrate Fru-6-P, which can lower the dissociation constant for Fru-2,6-BP 9-fold to 4 microM and that for Fru-1,6-BP 5-fold to 0.28 mM. These data are interpreted to suggest that influencing the aggregation state of rat liver phosphofructokinase may be one way in which Fru-2,6-BP achieves its effects on the enzyme in vivo.

The control of glycolysis and gluconeogenesis by protein phosphorylation.

Fructose 2,6-bisphosphate has been discovered as a potent stimulator of liver phosphofructokinase. It is also an inhibitor of fructose 1,6-biphosphatase and a stimulator of PPi: fructose 6-phosphate phosphotransferase from higher plants. It is formed from fructose 6-phosphate and ATP by a 6-phosphofructo 2-kinase and hydrolysed by a fructose 2,6-bisphosphatase. These two enzymes have very similar physicochemical properties and could not be separated from each other. They are substrates for cyclic-AMP-dependent protein kinase, which inactivates the first enzyme and activates the second.

The role of fructose 2,6-bisphosphate in the long-term control of phosphofructokinase in rat liver

The phosphofructokinase stabilizing factor, believed to be a peptide of molecular weight 3,800 (Dunaway G.A. and Segal H.L., 1976, J. Biol. Chem. 251, 2323–2329), shares many chemical and biological properties with fructose 2,6-bisphosphate. It co-migrated with it upon gel filtration in the molecular weight range 300–400 or 3,000–4,000 depending upon the ionic strength of the solution. Fructose 2,6-bisphosphate is the most potent phosphofructokinase stabilizing agent present in the liver of a fed rat. Its disappearance during fasting and diabetes could account for the faster rate of degradation of phosphofructokinase reported to occur under these conditions. The effect of starvation to decrease by 60% the phosphofructokinase content of the liver is, however, for its greatest part, related to a non-specific decrease in liver mass.

Metabolite-controlled phosphorylation of hepatic phosphofructokinase proceeds by cAMP-dependent protein kinase

In hepatocytes 32P-incorporation into rat liver phosphofructokinase is stimulated by glucose as well as by glucagon, the effects of both stimuli being prevented by L-alanine [Eur. J. Biochem. (1982) 122, 175]. The phosphopeptides of the enzyme derived from limited proteolysis by subtilisin and from exhaustive tryptic digestion were analyzed either by one-dimensional mapping on sodium dodecyl sulphate-polyacrylamide slab gels and by fingerprint mapping, respectively. It is shown that in vivo stimulation of 32P-incorporation by glucose or by glucose plus glucagon results in identical phosphopeptide maps, and that these maps were identical with those obtained from phosphofructokinase phosphorylated in vitro with catalytic subunit of cAMP-dependent protein kinase. It is concluded that in the intact liver cell phosphofructokinase is phosphorylated by cAMP-dependent protein kinase but that the state of phosphorylation is modified by metabolite control.

Purification of homogeneous rat phosphofructokinase isozymes with high specific activities

The purification of rat muscle and liver phosphofructokinase (PFK) isozymes has been greatly facilitated by column chromatographic separation on immobilized Cibacron Blue F 3GA. The homogeneous liver PFK isozyme exhibited a specific activity of greater than 200 units per mg of protein which is nearly two-fold greater than has been previously reported for this isozyme. The yields for this isozyme exceeded 40% of the original activity and the molecular weight of its subunit was about 85,000 as determined by SDS-polyacrylamide gel electrophoresis. The muscle PFK isozyme's specific activity was approximately 265 units/mg of protein which also is about twice the greatest specific activity previously reported. The overall yield for muscle PFK exceeded 50% of the original activity, and the molecular weight of its subunit was approximately 82,000. Using each homogeneous isozyme, antibodies were produced in rabbits; and the immunoglobin-G (IgG) fraction from the sera of these rabbits was highly specific for the PFK isozyme used as an antigen.

Age-related changes in activities of hepatic phosphofructokinase, pyruvate kinase and pyruvate dehydrogenase in liver and adipose tissue of the swiss albino mouse.

The activities of phosphofructokinase, pyruvate kinase and pyruvate dehydrogenase were examined in liver as a function of age in Swiss albino mice. The hepatic activity of phosphofructokinase and total pyruvate dehydrogenase peaked in mice between 8 and 12 weeks of age and then decreased to a value that remained stable in mature animals older than 24 weeks of age. Yet, the activity of pyruvate kinase and pyruvate dehydrogenase in the active form in liver remained unchanged in mice up to 12 weeks of age. As mice matured, a progressive increase in the activity of both pyruvate kinase and the active form of pyruvate dehydrogenase in liver was observed while phosphofructokinase was unaltered. The pyruvate dehydrogenase complex, both total activity and the proportion of the enzyme in the active form, in the epididymal fat pad of the mouse showed no consistent age trend. The observed increase in the activity of both pyruvate kinase and the active form of pyruvate dehydrogenase should provide an augmented capacity for the generation of acetyl-CoA units for de novo fatty acid synthesis in livers of mature mice.

Inactivation of phosphofructokinase in chicken hepatocytes by epinephrine

The effects of epinephrine on phosphofructokinase activity in hepatocytes from fed chickens were studied in crude extracts and after partial purification. The mechanism of epinephrine action was elucidated by use of phentolamine and penbutulol. Phosphofructokinase activity was decreased in extracts of cells exposed to epinephrine when measured at sub-saturating as well as saturating concentrations of fructose 6-phosphate. This effect was still present after filtration through Sephadex G25 gel and a subsequent precipitation with ammonium sulfate. Half-maximal effects of epinephrine were found in a concentration range between 10 −8 and 10 −7 M epinephrine. The effect of epinephrine was unaffected by Ca 2+ or the α-adrenergic antagonist phentolamine, and was abolished by the β-adrenergic antagonist penbutulol. We assume that the effects of epinephrine on the activity of chicken liver phosphofructokinase are mediated by a cAMP-dependent mechanism which cannot be explained by concentration shifts of low-molecular-mass substances such as fructose 2,6-bisphosphate.

Metabolite-controlled phosphorylation of phosphofructokinase in rat hepatocytes.

The effect of glucose on the phosphorylation of phosphofructokinase has been investigated in hepatocytes isolated froin fed and 24‐h‐starved rats by measuring the 32P radioactivity associated with the enzyme. In addition, the effects of gluconeogenic precursors and of glucagon or Bt2cAMP were followed under these conditions.The basal incorporation of phosphate into phosphofructokinase in hepatocytes from starved and fed rats was 0.2 ± 0.1 and 0.6±0.2 mol phosphate/mol phosphofructokinase (tetramer) respectively, whereas the maximal incorporation obtained was 1.03 ± 0.2 mol phosphate/mol phosphofructokinase.With 16 mM l‐lactate + 4 mM pyruvate or with 20 mM l‐alanine, the phosphorylation of the enzyme was lower than the basal incorporation found in hepatocytes from fed and starved rats.Glucose (20 mM) addition to isolated hepatocytes from fed rats resulted in an increase in the incorporation phosphate into phosphofructokinase to almost maximal value.In hepatocytes isolated from starved rats, glucose led to a 2.5‐fold increase of phosphorylation as compared to the basal incorporation. l‐Alanine (20 mM) abolished the glucose‐induced phosphorylation in hepatocytes from starved and from fed animals.Glucagon (0.1 μM) did not significantly enhance thc phosphorylation of phospliofructokinase in the presence of l‐lactate + pyruvate in hepatocytes from starved rats, but stimulated the phosphorylation to maximal value when cells had been preincubated in the presence of glucose.In contrast, in liver cells isolated from fed rats. glucagon had no additional effect on phosphofructokinase pliosphorylation in the presence of glucose, but did increase the phosphorylation to maximal value when l‐lactate + pyruvate served as substrates. l‐Alanine inhibited the glucose‐induced phosphorylation of phosphofructokinase also in the presence of glucagon.In contrast, glucagon stimulated the phosphorylation of l‐type pyruvate kinase independently from exogenous precursors and from the nutritional state of the animals.Bt2cAMP (0.1 mM) as glucagon, did not significantly enhance the phosphorylation of phosphofructokinase above the level obtained with glucose alone in hepatocytes from fed rats, but did increase the velocity of the phosphate incorporation in hepatocytes from starved rats, thus leading under both conditions to the maximal incorporation.It is concluded that the degree of phosphorylation of rat liver phosphofructokinase is affected by the metabolic state, and that glucagon (or CAMP) acts indirectly, probably by changing glucose metabolism due to increased glycogenolysis rather than by an activation of a CAMP‐dependent protein kinase.

Phosphofructokinase isozymes of Morris hepatomas

In this paper we demonstrate by DEAE-cellulose column chromatography, agarose gel electrophoresis, and immunological techniques that at least three phosphofructokinase (PFK) isozymes exist in Morris hepatomas regardless of their state of differentiation. The major PFK isozyme in Morris hepatomas was found to be the major liver PFK isozyme (PFK-L 2) which varied from approximately 4.7 units/g in poorly differentiated hepatomas to approximately 2.5 units/g in liver, as well as highly and well-differentiated hepatomas. One of the minor isozymes, the hepatoma type PFK (PFK-H), was not present in liver and was found by resolution of DEAE-cellulose chromatography and immunological studies to be greater in the poorly differentiated hepatomas (approximately 30%) compared to the well and highly differentiated hepatomas (5–10%). Further, immunological studies indicated that in the poorly differentiated hepatomas 25–30% of the total PFK activity could be precipitated by both PFK-L 2 and muscle type PFK (PFK-M) antisera. In order to examine this observation more closely, supernates from the poorly differentiated hepatoma 3924A were incubated with each type of antiserum. As shown by agarose gel electrophoresis, incubation with PFK-L 2 antiserum resulted in the loss of PFK-L 2 and PFK-H isozymes, whereas incubation with PFK-M antiserum resulted in the loss of PFK-H, and the other minor hepatoma PFK isozyme. These data indicate that PFK-M is one of the minor hepatoma isozymes and that the other, PFK-H, has common antigenic determinants with PFK-M and PFK-L 2.

Inactivation of liver phosphofructokinase by phosphofructokinase phosphatase or by low pH is inhibited by fructose 2,6-bisphosphate

FEBS LettersVolume 130, Issue 2 p. 309-313 Full-length articleFree Access Inactivation of liver phosphofructokinase by phosphofructokinase phosphatase or by low pH is inhibited by fructose 2,6-bisphosphate Correction(s) for this article Inactivation of liver phosphofructokinase by phosphofructokinase phosphatase or by low pH is inhibited by fructose 2,6-bisphosphate Volume 134Issue 1FEBS Letters pages: 123-123 First Published online: October 23, 2001 H.D. Söling, H.D. Söling Abt. für Klin. Biochemie, Zentrum Innere Medizin, Universität Göttingen, D-34 Göttingen, FRGSearch for more papers by this authorJ. Kuduz, J. Kuduz Abt. für Klin. Biochemie, Zentrum Innere Medizin, Universität Göttingen, D-34 Göttingen, FRGSearch for more papers by this authorI.A. Brand, I.A. Brand Abt. für Klin. Biochemie, Zentrum Innere Medizin, Universität Göttingen, D-34 Göttingen, FRGSearch for more papers by this author H.D. Söling, H.D. Söling Abt. für Klin. Biochemie, Zentrum Innere Medizin, Universität Göttingen, D-34 Göttingen, FRGSearch for more papers by this authorJ. Kuduz, J. Kuduz Abt. für Klin. Biochemie, Zentrum Innere Medizin, Universität Göttingen, D-34 Göttingen, FRGSearch for more papers by this authorI.A. Brand, I.A. Brand Abt. für Klin. Biochemie, Zentrum Innere Medizin, Universität Göttingen, D-34 Göttingen, FRGSearch for more papers by this author First published: August 03, 1981 https://doi.org/10.1016/0014-5793(81)81146-5Citations: 17AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume130, Issue2August 03, 1981Pages 309-313 ReferencesRelatedInformation