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N B Livanova

Publications and source records attributed to N B Livanova.

53 records · Page 3Linked to original sources
PubMed1977

[Isolation and properties of glycogen phosphorylase b from rabbit liver].

Purification of dephosphorylated form of rabbit liver glycogen phosphorylase (phosphorylase b) has been carried out. The purification procedure included 3 steps:sedimentation of protein-glycogen pellet by centrifugation at 62 000 x g during 2 hours, chromathography on omega-amino-hexyl-Sepharose column and isoelectric focusing. The yield of the enzyme is about 60%, the specific activity at glucose-1-phosphate concentration 100mM is 35 mkmol of Pi/mg protein-min. The final preparation revealed apparent homogeneity during ultracentrifugation and polyacrylamide gel electrophoresis. The subunit molecular weight of 100 000 was determined by disc-electrophoresis in the presence of sodium dodecyl sulfate. The absorption spectrum of liver phosphorylase b shows a protein maximum at 280 nm and a second peak at 333 nm produced by bound PLP. A kinetic analysis of initial rates with variable concentrations of the substrate revealed the homotropic cooperativity of glucose-1-phosphate binding sites. This cooperative effect is more pronounced in the presence of inhibitors, glucose and ATP and less pronounced in the presence of AMP.

Adenosine Monophosphate↗
PubMed1977

[Purification and kinetic properties of glycogen phosphorylase A from rabbit liver].

The purification of phosphorylated form of rabbit liver glycogen phosphorylase (phosphorylase A) using the chromathography on a omega-amino-hexyl-Sepharose column has been carried out. The yield is about 90%, the specific activity is equal to 90 mkmol Pi/min. mg. The enzyme samples appeared essentially homogeneous when analyzed by polyacrylamide gel electrophoresis. The Km value of glucose-1-phosphate in the presence of AMP is 4--6 mM, which is higher than that found previously. When the glucose-1-phosphate concentration was varied, deviations from Michaelis-Menten kinetics were observed in the presence of glucose or ATP (Hill slopes of 1.6), but these deviations were virtually abolished by the presence of AMP. With glucose-1-phosphate as the substrate the Ki value of glucose is 57 mM in the absence of AMP and 150 mM in the presence of this effector. The Ki value of ATP is less dependent on the presence of AMP. The synergism in combined action of glucose and ATP has been revealed.

Adenosine Monophosphate↗
PubMedDate not supplied

[Comparative study of the circular dichroism of rabbit liver and muscle glycogen phosphorylases a and b].

Circular dichroism (CD) spectra of glycogen phosphorylase a and b from rabbit liver have been measured in the presence of various ligands in the near- and far-ultraviolet regions. Positive circular dichroism was detected in the absorption band of protein-bound pyridoxal phosphate (333 nm). The mean residue ellipticity of this dichroic band (35 deg cm2dmol-1) is of the same order for muscle and liver phosphorylase a and b and does not change upon binding of glucose-1-phosphate and AMP. Only glucose induces small changes in the ellipticity in this region. The CD spectra of muscle and liver phosphorylase a and b in the 250-300 nm region have at least five positive dichroic bands namely at 259, 264, 273, 281 and 288 nm and have strong resemblances for all these forms of the enzyme in spite of the fundamental differences in their properties. The binding of AMP and glucose to phosphorylase from both sources induces distinct perturbations in CD spectra; the changes are much larger for muscle and liver phosphorylase a than for phosphorylase b which indicates that conformational perturbations induced by binding of activator and inhibitor to the inactive form of phosphorylase are probably more local than for the active form. The CD spectra in far-ultraviolet region are similar for all forms of phosphorylase. The percent of alpha-helices calculated according to Chen is about 50; this value coincides very well with the value 51% received for muscle phosphorylase a by X-ray crystallographic analysis at 2.5 A resolution.

Adenosine Monophosphate↗
PubMedDate not supplied

[Regulation of enzyme activity in adsorptive enzyme systems. III. Interaction of pig muscle lactate dehydrogenase with F-actin].

The binding of pig skeletal muscle lactate dehydrogenase by F-actin has been studied using the sedimentation method in 10 mM Tris-acetate buffer, pH 6.0 at 20 degrees C. Adsorption capacity of F-actin is equal to (1 +/- 0.1) . 10(-5) moles of lactate dehydrogenase per 1 g of actin. NADH decreases the affinity of F-actin with respect to lactate dehydrogenase. The binding of lactate dehydrogenase by F-actin in diminishing the rate of enzymatic reduction of alpha-ketoglutarate. The microscopic dissociation constant for the complex of the enzyme with F-actin which is estimated from the dependence of the enzymatic reaction rate of F-actin concentration at saturating NADH concentrations is equal (3.0 +2- 0.5) . 10(-7) M. It has been shown that the bound enzyme is characterized by the greater value of Km and the lower value of Vmax in comparison to the free enzyme.

Actins↗
PubMedDate not supplied

[The effect of specific deimination of glycogen phosphorylase b by peptidylarginine deiminase on the allosteric properties of the enzyme and dimer-tetramer transition].

The kinetics of the native glycogen phosphorylase b from rabbit skeletal muscle and of the enzyme specifically deiminated by peptidylarginine deiminase have been studied. According to the data on amino acid composition one arginine residue per phosphorylase b monomer is transformed into citrulline after 3 hours of incubation with peptidylarginine deiminase. The kinetics of the phosphorylase reaction were studied in the direction of glycogen synthesis. The native and the deiminated forms of phosphorylase b showed similar affinity to glucose 1-phosphate. The maximal velocity of the enzymatic reaction for the modified phosphorylase b is 8-20% higher than that for the native enzyme. Deiminated phosphorylase b like the native enzyme shows a positive kinetic cooperatively with respect to glucose 1-phosphate in the presence of the allosteric inhibitors (FMN, glucose), S-shaped dependences of the velocity of the enzymatic reaction on glucose 1-phosphate concentration (in the presence of FMN) pronouncing more distinctly for deiminated phosphorylase b than for the native enzyme (Hill coefficient is equal to 1.7 +/- 0.2 and 1.3 +/- 0.1, respectively). The affinity of the modified phosphorylase b to the allosteric activator AMP is one order of magnitude higher than that to the native enzyme. The cooperativity of AMP binding doesn't change significantly after deimination. The kinetics of inhibition of the native and modified phosphorylase b by FMN, glucose and glucose 6-phosphate are cooperative (the value of Hill coefficient is higher than unity). The more pronounced distinctions between two forms of the enzyme concern with the value of the "semisaturation" concentration [I]0.5. The deimination causes a pronounced reduction of the values of [I]0.5 for FMN and glucose, but the sensitivity of the deiminated enzyme to glucose 6-phosphate is much lower than that of the native phosphorylase b. Deiminated phosphorylase b unlike the native enzyme shows the positive cooperativity of the FMN binding (the value of the Hill coefficient is equal to 1.37 +/- 0.05). Deiminated phosphorylase b shows less capability to form tetramer in the presence of AMP as compared to the native enzyme.

Allosteric Regulation↗