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At least 325 records · Page 18Linked to original sources
PubMed1983

The interaction of fructose 2,6-bisphosphate with an allosteric site of rat liver fructose 1,6-bisphosphatase.

Rat liver fructose 1,6-bisphosphatase can be protected against partial inactivation by N-ethylmaleimide by low concentrations of fructose 2,6-bisphosphate or high concentrations of fructose 1,6-bisphosphate. The partially inactivated enzyme has a much reduced sensitivity to high substrate inhibition and has lost the sigmoid component of the inhibition by fructose 2,6-bisphosphate; this compound is a simple linear competitive inhibitor of the modified enzyme. The results suggest that fructose 2,6-bisphosphate can bind to the enzyme at two distinct sites, the catalytic site and an allosteric site. High levels of fructose 1,6-bisphosphate probably inhibit by binding to the allosteric site.

Allosteric Regulation↗
PubMed1984

Biphasic effect of fructose 2,6-bisphosphate on the liver fructose-1,6-bisphosphatase: mechanistic and physiological implications.

Fructose 2,6-bisphosphate has been claimed to be both a substrate analogue and an allosteric inhibitor of fructose-1,6-bisphosphatase. The results reported here show that fructose 2,6-bisphosphate can be both an inhibitor and an activator of the enzyme, depending on the substrate concentration. This biphasic behaviour at saturating concentrations of substrate can only be due to an allosteric effect. In addition to the mechanistic implication it is possible that this finding may have physiological meaning.

Animals↗
PubMed1984

The effect of fructose 2,6-bisphosphate and AMP on the activity of phosphorylated and unphosphorylated fructose-1,6-bisphosphatase from rat liver.

Rat liver fructose-1,6-bisphosphatase was partially phosphorylated in vitro and separated into unphosphorylated and fully phosphorylated enzyme. The effects of fructose 2,6-bisphosphate and AMP on these two enzyme forms were examined. Unphosphorylated fructose-1,6-bisphosphatase was more easily inhibited by both effectors. Fructose 2,6-bisphosphate affected both K0.5 and Vmax, while the main effect of AMP was to lower Vmax. Fructose 2,6-bisphosphate and AMP together acted synergistically to decrease the activity of fructose-1,6-bisphosphatase, and since unphosphorylated and phosphorylated enzyme forms are affected differently, this might be a way to amplify the effect of phosphorylation.

Adenosine Monophosphate↗
PubMed1984

Fructose 2,6-bisphosphate, sugar phosphates and adenine nucleotides in the regulation of glucose metabolism in the lactating rat mammary gland.

Fructose 2,6-bisphosphate is present in the rat mammary gland, rising from a value of 1.4 nmol/g in pregnancy to 4.3 nmol/g tissue at 14 days lactation; the equivalent values calculated/ml intracellular water are 5.2 and 11.6 nmol, respectively. The tissue content of fructose 6-phosphate, fructose 1,6-bisphosphate, ATP and phosphoenolpyruvate remain relatively constant in the transition from pregnancy to the height of lactation. The changes in AMP, cyclic AMP, and citrate content of the mammary gland during lactation are such as to promote an increase in fructose 2,6-bisphosphate formation and flux through phosphofructokinase.

Adenosine Monophosphate↗
PubMed1984

The effect of insulin on Fru-2,6-P2 levels in human fibroblasts.

We report that fructose 2,6-bisphosphate (Fru-2,6-P2) levels in quiescent human fibroblasts stimulated with insulin treatment increase in a time- and dose-dependent manner. The biochemical role of the sugar phosphate in the cellular response to the hormone which controls carbohydrate metabolism and acts as mitogenic factor is discussed.

Cells, Cultured↗
PubMed1984

Activation of rat heart phosphofructokinase-2 by insulin in vivo.

Fifteen minutes after the intravenous injection of overnight starved, anaesthetized rats with insulin, the concentration of fructose 2,6-biphosphate was increased more than 2-fold in the hearts of these animals. Insulin injection also caused a 2-3 fold increase in the Vmax of phosphofructokinase-2 with no detectable change in Km values. The effect persisted after precipitation of the enzyme with polyethylene glycol or after gel filtration through Sephadex G-25.

Animals↗
PubMed1985

Hormonal regulation of fructose 2,6-bisphosphate levels in epididymal adipose tissue of rat.

The participation of fructose 2,6-bisphosphate on glycolysis stimulated by insulin and adrenaline in incubated white adipose tissue of rat was investigated. Adrenaline addition to incubated fat-pads strongly decreased the intracellular levels of fructose 2,6-bisphosphate. When the tissue was preincubated with glucose, the presence of insulin in the incubation medium increased fructose 2,6-bisphosphate levels 2-fold. These variations were related to changes in the substrates, ATP and fructose 6-phosphate. It therefore appears that fructose 2,6-bisphosphate may be involved in the control of insulin-induced glycolysis, but it does not seem to play a role in the stimulation of glucolysis by adrenaline.

Adenosine Triphosphate↗
PubMed1986

Fructose 2,6-bisphosphate and the control of glycolysis in bovine spermatozoa.

Epididymal bovine sperm contain fructose-1,6-bisphosphatase activity which is inhibited by AMP and by fructose 2,6-bisphosphate. Sperm phosphofructokinase displays kinetic characteristics that are typical of the F-type and it is stimulated by fructose 2,6-bisphosphate. The concentration of sperm fructose 2,6-bisphosphate remained unaffected at 1-2 microM when the glycolytic rate was either increased by glucose, caffeine or antimycin, or decreased by alpha-chlorohydrin or 6-chloro-6-deoxyglucose.

Animals↗
PubMed1986

Mechanism of glucagon stimulation of fructose-1,6-bisphosphatase in rat hepatocytes. Involvement of a low-Mr activator.

Isolated rat hepatocytes were incubated in the absence or presence of glucagon and the activity of fructose-1,6-bisphosphatase was measured in cell extracts. After glucagon treatment the Vmax was increased (20-50%) whereas the Km remained unchanged. The stimulation was complete at 5 min after addition of glucagon. The glucagon concentration needed for maximal stimulation was 10(-9) M. After gel filtration the fructose-1,6-bisphosphatase activity in extracts of glucagon-treated cells was lowered to the control level. The effect of glucagon could not be completely mimicked by dibutyryl cAMP. The data indicate that in addition to the possible regulatory role of enzyme phosphorylation, a positive effector is involved in the stimulation of fructose-1,6-bisphosphatase activity by glucagon.

Animals↗