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Biomedical subjects

K Uyeda

Publications and source records attributed to K Uyeda.

At least 73 records · Page 4Linked to original sources
PubMed1983

Significance of phosphorylation of phosphofructokinase.

In order to understand the effect of phosphorylation on phosphofructokinase, the allosteric kinetic behavior, ligand binding at various pHs, and pH-dependent cold inactivation of phosphofructokinase phosphorylated to different extents were studied. A subtilisin-digested phosphofructokinase from which a COOH-terminal peptide containing a phosphorylation site has been cleaved (Riquelme, P. T., and Kemp, R. G. (1980) J. Biol. Chem. 255, 4367-4371) was also included in these studies in order to investigate the possible role of this region of the molecule. Allosteric kinetics and direct binding experiments have shown that increasing phosphorylation of phosphofructokinase results in increased sensitivity to ATP inhibition and stronger binding of ATP to the inhibitory site of the enzyme. Ths subtilisin-cleaved phosphofructokinase is the least sensitive to the inhibition and shows the weakest binding of ATP. The opposite effect is observed with the binding isotherms of fructose-6-P. There is no difference in the binding of fructose-2,6-P2 among these enzymes. Binding of ATP to the inhibitory site of these enzymes as determined by fluorescence quenching (Pettigrew, D. W., and Frieden, C. (1979) J. Biol. Chem. 254, 1887-1895) is affected by pH; the binding is greatly enhanced at lower pH. Moreover, there is little difference in the binding among the modified enzymes at pH 8, but at lower pHs the binding to the phosphorylated enzyme is much more enhanced than the dephosphoenzyme. A pH-dependent cold inactivation study has shown that the phosphorylation of the enzyme causes an increase in the pK value for the inactivation, and the extent of the pK shift depends upon the degree of phosphorylation. Based on these results, a model originally proposed by Frieden et al. (Frieden, C., Gilbert, H. R., and Bock, P. E. (1976) J. Biol. Chem. 251, 5644-5647) can be applied to explain a possible role for the phosphorylation and the peptide portion of phosphofructokinase in its complex allosteric kinetic behavior.

Allosteric Regulation↗
PubMed1983

Differences in the allosteric properties of pure low and high phosphate forms of phosphofructokinase from rat liver.

Low phosphate and high phosphate forms of phosphofructokinase (Furuya, E., and Uyeda, K. (1980) J. Biol. Chem. 255, 11656-11659) from rat liver were purified to homogeneity and various properties were compared. The specific activities of these enzymes and their electrophoretic mobilities on polyacrylamide in sodium dodecyl sulfate are the same. A limited tryptic digestion yields products with no change in the enzyme activity but with a reduction in the molecular weight of about 2000. Both low and high phosphate enzymes can be phosphorylated by the catalytic subunit of cAMP-dependent protein kinase, and approximately twice as much [32P]phosphate is incorporated into the low phosphate than the high phosphate enzyme. A comparison of their allosteric kinetic properties reveal that the high phosphate enzyme is much more sensitive to inhibition by ATP and citrate and shows a higher K0.5 for fructose 6-phosphate than the low phosphate enzyme, and the difference in the K0.5 values becomes greater at lower pH values. Furthermore, the high phosphate phosphofructokinase is less sensitive to activation by AMP and fructose 2,6-bisphosphate. Moreover, when the low phosphate enzyme is phosphorylated by protein kinase, the resulting phosphorylated enzyme exhibits a higher K0.5 for fructose 2,6-bisphosphate than does the untreated enzyme. These results demonstrate that the phosphorylation affects the allosteric kinetic properties of the enzyme and results in a less active form of phosphofructokinase.

Adenosine Monophosphate↗
PubMed1983

A binding study of the interaction of beta-D-fructose 2,6-bisphosphate with phosphofructokinase and fructose-1,6-bisphosphatase.

The binding of beta-D-fructose 2,6-bisphosphate to rabbit muscle phosphofructokinase and rabbit liver fructose-1,6-bisphosphatase was studied using the column centrifugation procedure (Penefsky, H. S., (1977) J. Biol. Chem. 252, 2891-2899). Phosphofructokinase binds 1 mol of fructose 2,6-bisphosphate/mol of protomer (Mr = 80,000). The Scatchard plots of the binding of fructose 2,6-bisphosphate to phosphofructokinase are nonlinear in the presence of three different buffer systems and appear to exhibit negative cooperativity. Fructose 1,6-bisphosphate and glucose 1,6-bisphosphate inhibit the binding of fructose-2,6-P2 with Ki values of 15 and 280 microM, respectively. Sedoheptulose 1,7-bisphosphate, ATP, and high concentrations of phosphate also inhibit the binding. Other metabolites including fructose-6-P, AMP, and citrate show little effect. Fructose-1,6-bisphosphatase binds 1 mol of fructose 2,6-bisphosphate/mol of subunit (Mr = 35,000) with an affinity constant of 1.5 X 10(6) M-1. Fructose 1,6-bisphosphate, fructose-6-P, and phosphate are competitive inhibitors with Ki values of 4, 2.7, and 230 microM, respectively. Sedoheptulose 1,7-bisphosphate (1 mM) inhibits approximately 50% of the binding of fructose 1,6-bisphosphate to fructose bisphosphatase, but AMP has no effect. Mn2+, Co2+, and a high concentration of Mg2+ inhibit the binding. Thus, we may conclude that fructose 2,6-bisphosphate binds to phosphofructokinase at the same allosteric site for fructose 1,6-bisphosphate while it binds to the catalytic site of fructose-1,6-bisphosphatase.

Animals↗
PubMed1982

Fructose-2,6-P2, chemistry and biological function.

A new activator of phosphofructokinase, which is bound to the enzyme and released during its purification, has been discovered. Its structure has been determined as beta-D Fructose-2,6-P2 by chemical synthesis, analysis of various degradation products and NMR. D-Fructose-2,6-P2 is the most potent activator of phosphofructokinase and relieves inhibition of the enzyme by ATP and citrate. It lowers the Km for fructose-6-P from 6 mM to 0.1 mM. Fructose-6-P,2-kinase catalyzes the synthesis of fructose-2,6-P2 from fructose-6-P and ATP, and the enzyme has been partially purified. The degradation of fructose-2,6-P2 is catalyzed by fructose-2,6-bisphosphatase. Thus a metabolic cycle could occur between fructose-6-P and fructose-2,6-P2, which are catalyzed by these two opposing enzymes. The activities of these enzymes can be controlled by phosphorylation. Fructose-6-P,2-kinase is inactivated by phosphorylation catalyzed by either cAMP dependent protein kinase or phosphorylase kinase. The inactive, phospho-fructose-6,P,2-kinase is activated by dephosphorylation catalyzed by phosphorylase phosphatase. On the other hand, fructose-2,6-bisphosphatase is activated by phosphorylation catalyzed by cAMP dependent protein kinase. Investigation into the hormonal regulation of phosphofructokinase reveals that glucagon stimulates phosphorylation of phosphofructokinase which results in decreased affinity for fructose-2,6-P2 appears to be due to the decreased synthesis by inactivation of fructose-2,6-P2,2-kinase and increased degradation as a result of activation of fructose-2,6-bisphosphatase. Such a reciprocal change in these two enzymes has been demonstrated in the hepatocytes treated by glucagon and epinephrine. The implications of these observations in respect to possible coordinated controls of glycolysis and glycogen metabolism are discussed.

Enzyme Activation↗
PubMed1982

A special fructose bisphosphate functions as a cytoplasmic regulatory metabolite in green leaves.

Fructose 2,6-bisphosphate (Fru-2,6-P(2)), a regulatory metabolite discovered in animal cells and recently reported to occur in etiolated seedlings, was found to be present in the cytoplasmic fraction of leaves of spinach and peas (typical C(3) plants, in which a three-carbon carboxylic acid is a major early photosynthetic product). At concentrations approximating those calculated to occur physiologically, Fru-2,6-P(2) modulated two enzymes of the leaf cytoplasm: (i) Fructose-1,6-bisphosphatase (EC 3.1.3.11), a key enzyme of sugar synthesis, was competitively inhibited by Fru-2,6-P(2), and (ii) pyrophosphate-linked phosphofructokinase (inorganic pyrophosphate-D-fructose-6-phosphate 1-phosphotransferase, EC 2.7.1.90), a cytoplasmic enzyme that now seems important in glycolysis of C(3) plants, was activated by Fru-2,6-P(2). There was no indication of a role for Fru-2,6-P(2) in photosynthesis of either chloroplasts or oxygenic prokaryotes. The results suggest that Fru-2,6-P(2) functions in the regulation of glycolysis and gluconeogenesis (carbohydrate synthesis) in the cytoplasm of leaves of C(3) plants.

Journal Article↗
PubMed1982

Regulation of fructose-6-phosphate 2-kinase by phosphorylation and dephosphorylation: possible mechanism for coordinated control of glycolysis and glycogenolysis.

The kinetic properties and the control mechanism of fructose-6-phosphate 2-kinase (ATP: D-fructose-6-phosphate 2-phosphotransferase) were investigated. The molecular weight of the enzyme is approximately 100,000 as determined by gel filtration. The plot of initial velocity versus ATP concentration is hyperbolic with a Km of 1.2 mM. However, the plot of enzyme activity as a function of fructose-6-phosphate is sigmoidal. The apparent K0.5 for fructose-6-phosphate is 20 microM. Fructose-6-phosphate 2-kinase is inactivated by the catalytic subunit of cyclic AMP-dependent protein kinase, and the inactivation is closely correlated with phosphorylation. The enzyme is also inactivated by phosphorylase kinase in the presence of Ca2+ and calmodulin. The phosphorylated fructose-6-phosphate 2-kinase, which is inactive, is activated by phosphorylase phosphatase and alkaline phosphatase. The possible physiological significance of these observations in the coordinated control of glycogen metabolism and glycolysis is discussed.

Calcium↗
PubMed1981

The effect of natural and synthetic D-fructose 2,6-bisphosphate on the regulatory kinetic properties of liver and muscle phosphofructokinases.

The effect of natural "activation factor" and synthetic fructose-2,6-P2 on the allosteric kinetic properties of liver and muscle phosphofructokinases was investigated. Both synthetic and natural fructose-2,6-P2 show identical effects on the allosteric kinetic properties of both enzymes. Fructose-2,6-P2 counteracts inhibition by ATP and citrate and decreases the Km for fructose-6-P. This fructose ester also acts synergistically with AMP in releasing ATP inhibition. The Km values of liver and muscle phosphofructokinase for fructose-2,6-P2 in the presence of 1.25 mM ATP are 12 milliunits/ml (or 24 nM) and 5 milliunits/ml (or 10 nM), respectively. At near physiological concentrations of ATP (3 mM) and fructose-6-P (0.2 mM), however, the Km values for fructose-2,6-P2 are increased to 12 microM and 0.8 microM for liver and muscle enzymes, respectively. Thus, fructose-2,6-P2 is the most potent activator of the enzyme compared to other known activators such as fructose-1,6-P2. The rates of the reaction catalyzed by the enzymes under the above conditions are nonlinear: the rates decelerate in the absence or in the presence of lower concentrations of fructose-2,6-P2, but the rates become linear in the presence of higher concentrations of fructose-2,6-P2. Fructose-2,6-P2 also protects phosphofructokinase against inactivation by heat. Fructose-2,6-P2, therefore, may be the most important allosteric effector in regulation of phosphofructokinase in liver as well as in other tissues.

Adenosine Monophosphate↗
PubMed1981

The structure of "activation factor" for phosphofructokinase.

The "activation factor" for phosphofructokinase was shown by chemical analysis, by synthesis, and by 13C NMR spectroscopy to be beta-D-fructose-2,6-P2. This compound was prepared from D-fructose-1,2-cyclic 6-P2 by alkaline hydrolysis. D-Fructose-1,2-cyclic 6-P2 is ineffective in activating phosphofructokinase while synthetic D-fructose-2,6-P2 has the same specific activity toward phosphofructokinase as the "activation factor" isolated from rat liver, and it exhibits the same characteristics on paper and ion exchange chromatography. Acid treatment of both the synthetic and the natural product destroys the biological activity and yields 1 mol each of fructose-6-P and Pi; alkaline phosphatase treatment of the compound followed with acid hydrolysis yields fructose. The natural abundance 13C NMR spectra of the synthetically prepared and purified D-fructose-1,2-cyclic 6-P2 and D-fructose-2,6-P2 have been obtained and all resonances have been assigned. The spectra also show that both samples contain predominantly one anomer and the 13C chemical shifts and 31P-13C coupling constants are consistent only with the beta-anomer.

Animals↗
PubMed1981

A novel enzyme catalyzes the synthesis of activation factor from ATP and D-fructose-6-P.

We have recently discovered an activator for phosphofructokinase termed "activation factor" (Furuya, E., and Uyeda, K. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 5861-5864). In this paper, we investigated the enzyme responsible for its synthesis. We have found an enzyme from rat liver which catalyzes the formation of activation factor from fructose-6-P and ATP-Mg and it has been identified as fructose-2,6-P2. Fructose-1,6-P2, fructose-1-P, or fructose does not serve as a substrate. This enzyme has been partially purified and shown to be different from phosphofructokinase. Several lines of evidence indicate that the in vitro synthetic product is identical with chemically synthesized fructose-2,6-P2: (a) it is active in our assay for activation factor which is based on counteraction of ATP inhibition of phosphofructokinase; (b) it is acid labile as is fructose-2,6-P2; and (c) it shows the same mobility as synthetic fructose-2,6-P2 upon paper chromatography and the acid hydrolysis product has been identified as fructose-6-P. Thus, this new enzyme catalyzes the synthesis of the activation factor from fructose-6-P and ATP-Mg.

Adenosine Triphosphate↗