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At least 955 records · Page 53Linked 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↗
PubMed1990

Could domain movements be involved in the mechanism of trypsin-like serine proteases?

It is hypothesised that the characteristic twin domain structure of serine proteases permits important allosteric responses in the molecule when peptide and protein substrates bind. Such movement would be ideal for stressing the scissile bond in the substrate, thereby making the task of hydrolysis substantially easier. The control of the domain movement can be closely associated with substrate binding, via the N- and C-terminal regions of the enzyme. The hypothesis also suggests that certain inhibitory peptides exert their effect by binding without inducing the domain movement.

Allosteric Regulation↗
PubMed1990

Decrease in cytoskeleton-bound phosphofructokinase in muscle induced by high intracellular calcium, serotonin and phospholipase A2 in vivo.

1. Particulate (cytoskeleton-bound) and soluble phosphofructokinase (PFK), separated from rat muscle, exhibited different allosteric properties; in contrast to the soluble PFK, the bound enzyme was not sensitive to allosteric regulation. 2. Treatment of muscle with Ca2(+)-ionophore A23187, serotonin, or phospholipase A2, reduced the binding of PFK and aldolase. 3. The decrease in enzymes' binding was most probably mediated by the rise in free intracellular Ca2+ induced by these agents, as we found that direct addition of Ca2+ to the particulate fraction of muscle, caused solubilization of bound PFK and aldolase. 4. The reduction in binding of PFK and aldolase to cytoskeletal proteins, may have a deleterious effect on muscle function and structure, and may be involved in the mechanism of muscle damage in pathological conditions where accumulation of Ca2+ occurs.

Animals↗
PubMed1990

Free energy of ATP-hydrolysis fails to affect ATP-dependent potassium channels in isolated mouse ventricular cells.

The single channel recording technique has been used to study the adenosine-5'-triphosphate (ATP)-dependent K+ channel in isolated mouse ventricular cells. The aim of this work was to determine if the activity of the K+ channel depends on the free energy of ATP-hydrolytic reaction (phosphorylation potential) in addition to the well-studied direct block by ATP. When the phosphorylation potential was changed from 60 to 50, to 40 and back to 60 kJ/mol at a constant ATP-concentration of 10(-4) mol/l, the ATP-channel activity showed a run down that is best described by a linear function. Changing the ATP-concentration of the bath solution from 0.01 to 1 and back to 0.01 mmol/l by a factor of 10 at a constant phosphorylation potential of 50 kJ/mol, resulted in a run down of the mean average current by a reduction of the open state probability in a concentration dependent manner. A dissociation constant of about 0.14 mmol/l could be estimated. The amplitude of the single channel current was not affected by ATP-concentrations in contrast to changes in phosphorylation potential. A significant increase in the single channel current accompanying a decrease in the phosphorylation potential at constant ATP concentrations was observed. This effect might be due to a decrease of free Mg2(+)-concentration by an increase of the ADP concentration in solutions with lower phosphorylation potentials. An allosteric regulation of the ATP-dependent K+ channel dependent on the free ATP concentration together with the Mg2(+)-ADP concentration seems to be a more likely explanation than regulation by phosphorylation/dephosphorylation secondary to a breakdown of ATP.

Action Potentials↗
PubMed1986

Co-operativity and enzymatic activity in polymer-activated enzymes. A one-dimensional piggy-back binding model and its application to the DNA-dependent ATPase of DNA gyrase.

The binding of a ligand to a one-dimensional lattice in the presence of a second ("rider") ligand, which binds only to the first ligand (piggy-back binding), is studied. A model derived from this study is used to analyze the effects of co-operativity on the reaction rates of enzymes activated by polymeric cofactors that provide multiple binding sites for the enzyme. It is found that in the presence of strong co-operativity, the steady-state reaction rates of polymer-activated enzymes can be very different from the Michaelis-Menten paradigm. By adjusting the co-operativity parameters and the binding constants of the ligands, the model can generate apparent auto-catalytic enhancement by substrates at low substrate concentrations and apparent substrate inhibition at high substrate concentrations. The model is shown to be able to explain the differences in the rates of ATP hydrolysis by DNA gyrase in the presence of long versus short DNA molecules and in the presence of long DNA molecules at different gyrase to DNA ratios.

Adenosine Triphosphatases↗
PubMed1983

Specific ligand-induced association of an enzyme. A new model of dissociating allosteric enzyme.

The kinetic behavior of dissociative enzyme system of the type inactive monomer in equilibrium active dimer where dimeric form is stabilized by specific ligand (in particular by substrate) which is bound in the region of the contact of monomers has been analysed. It is assumed that the dissociation of dimer results in formation of monomers which retain the subsites for specific ligand binding. The shape of the dependences of enzyme reaction rate (v) on substrate concentration (S) has been characterized using the order of enzyme reaction rate with respect to substrate concentration: ns = d ln v/d ln [S]. When the substrate concentrations are low the dependences of v on [S] have S-shaped form (the maximum value of ns exceeds the unity) at the definite values of the parameters of the enzyme system. The value of ns approaches--2 at sufficiently high substrate concentrations (in the region where the substrate reveals the inhibitory effect due to blocking the association of inactive monomers into active dimer). The methods of calculation of the parameters of the dissociative enzyme system under discussion have been elaborated on the basis of the analysis of the experimental dependences of specific enzyme activity on enzyme concentration obtained at various fixed substrate concentrations.

Allosteric Regulation↗