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Z S Kagan

Publications and source records attributed to Z S Kagan.

At least 19 recordsLinked to original sources
PubMed1985

[Complex type of kinetics of fructose-1,6-diphosphate from the rat and rabbit liver].

Studies on rat and rabbit liver fructose 1.6-bisphosphatase inhibition by AMP showed that with an increase in EDTA concentration the hyperbolic AMP inhibition curve is transformed into a sigmoidal one. At intermediate EDTA concentrations, the kinetic curves have a plateau. The appearance of the intermediate plateau may be due to the superposition of kinetic curves corresponding to two enzyme forms simultaneously present in the assay mixture. One of these forms deprived of endogenous Me2+ (presumably Zn2+) is inhibited by AMP in a cooperative manner, while the other one retains Me2+ which prevents the cooperative response of the enzyme to AMP.

Adenosine Monophosphate↗
PubMed1984

[Kinetic and allosteric properties of highly-purified, biosynthetic L-threonine dehydrogenase from brewer's yeast Saccharomyces carlsbergensis].

Kinetic and allosteric propeties of highly purified "biosynthetic" L-threonine dehydratase from brewer's yeast S. carlbergensis were studied at three pH values, using L-threonine and L-serine as substrates. It was shown that the plot of the initial reaction rate (v) versus initial substrate concentrations ([S]0 pH 6.5 is hyperbolic (Km=5.0.10-2M), while these at pH 7.8 and 9.5 have a faintly pronounced sigmoidal shape with fast occurring saturation plateaus ([S]0.5= 1.0.10-2 and 0.9.10-2M, respectively). the ratios between L-threonine and L-serine dehydratation rates depend on pH. The kinetic properties and the dependence of substrate specificity on pH suggest that the enzyme molecule undergoes pH-induced (at pH 7.0) conformational changes. The determination of pK values of the enzyme functional groups involved in L-threonine binding demonstrated that these groups have pK is approximately equal to 7.5 and 9.5. The latter group was hypothetically identified as a epsilon-NH2-group of the lysine residue. High concentrations of the allosteric inhibitor (L-isoleucine) decrease the rates of L-threonine and L-serine dehydratation and induce the appearance (at pH 6.5) or increase (at pH 7.9 and 9.5) of homotropic cooperative interactions between the active sites in the course of L-threonine dehydratation. The enzyme inhibition by L-isoleucine increases with a decrease of L-threonine concentrations. Low L-isoleucine concentrations, as well as the enzyme activator (L-valine) stimulate the enzyme at non-saturating substrate concentrations (when L-threonine or L-serine are used as substrates) without normalization of (v) versus [S]0 plots. The maximal activation of the enzyme is observed at pHG 8.5--9.0. It is assumed that the molecule of "biosynthetic" L-threonine dehydratase from brewer's yeast contains two types of sites responsible for the effector binding, i.e., "activatory" and "inhibitory" ones.

Alcohol Oxidoreductases↗
PubMed1983

Purification of commercial preparations of NADP+ from AMP contamination.

A method for purification of commercial preparations of NADP+ from AMP contamination is described. The purification procedure includes one-step anion-exchange chromatography on Dowex-1 (formate) and results in a highly purified salt-free coenzyme with a yield of 70-80%. The chromatography conditions have been selected allowing for complete separation of AMP from NADP+ in a HCOOH concentration gradient. This is followed by NADP+ elution with 1.5 M HCOOH containing HCOOK at a concentration at which the salt remains in solution during subsequent precipitation and washing of NADP+ with acetone. An addition of HCOOK is necessary to reduce the coenzyme elution volume that is important for further precipitation of NADP+ with acetone.

Adenosine Monophosphate↗
PubMed1981

[Comparative properties of multiple forms of rabbit muscle phosphofructokinase].

Some properties of three interconvertible forms of rabbit muscle phosphofructokinase specifically eluted from DEAE-cellulose with 19 mM citrate in 0.1 M tris-phosphate buffer, pH 8,0 (I), with 0,3 M buffer (II) and 1.5 M NaCl (III) are compared. Forms I-III differ in specific activities, alpha-helices content and sedimentation properties. The kinetic behaviour of forms I and III in 25 mM glycylglycine-beta-glycerophosphate, pH 8.3, at inhibitory ATP concentrations is characterized by biphasic velocity versus fructose-6-phosphate concentration curves with nH = 1.0 and 2.3, but with different V and [S]0.5 for the respective forms. At pH 6.8 from I is characterized by the kinetic curves with a lag period, while form III--by that with a burst. Form I reveals negative cooperativity in initial and stationary velocities at low substrate concentrations. The stationary velocity of form III is characterized by negative cooperativity within the whole concentration range studied. At pH 7.0 both forms are inhibited by citrate according to the initial and stationary velocities; however, the Ki values are different. The complex kinetic behaviour of phosphofructokinase corresponds to its complex chromatographic and sedimentation behaviour. The multiplicity of the enzyme forms seems to be due to a complex set of its oligomers and conformers and a hysteretic type of transitions between them as well as to its phosphorylation and possible binding of ligands.

Animals↗
PubMed1980

[Choice of the association model of rabbit muscle phosphofructokinase using mathematical modeling].

The sedimentation behaviour of the subform of rabbit muscle phosphofructokinase specifically eluted from DEAE cellulose by citrate was studied in different media by velocity experiments. The measured sedimentation coefficients of different components in the system can be classified into 12 groups, which is indicative of a complex multistep association process of the enzyme (with more than 3 oligomers). The concentration dependence of weight average sedimentation coefficient of phosphofructokinase was a studied. The choice of the probable association model of phosphofructokinase oligomers at low protein concentration was accomplished by means of computer simulation of the association process. Of 26 closed association models tested 14 models with 2 or 3 association constants are indistinguishable in view of Student's t-criterion of significance. All uniparametric association models studied significantly inferior approximate the experimental data. It is supposed that the dimer is not the structural unit of polymerization. Having this in mind and taking into account the demand for the multistep process, one may consider as most probable only 8 models of phosphofructokinase association, namely monomer-dimer-trimer-tetramer-monomer-dimer-tetramer-octamer (with 3 association constants) and linear polymerization up to the octamer with 2 association constants, where the "monomer" of association may be defined as trimer, tetramer or hexamer of subunits.

Animals↗
PubMed1979

[Comparative kinetic properties of structure-bound and solubilized L-threonine dehydratase from brewer's yeast].

It has been shown that L-threonine dehydratase (EC 4.2.1.16) of brewer's yeast Saccharomyces carlsbergensis is localized in the mitochondrial fraction. The enzyme is easily solubilized from the mitochondria by changing the pH and ionic strength of the buffer. Some kinetic properties of structure-bound and solubilized L-threonine dehydratase have been compared at pH 6,5. The kinetic plots of the initial rate of the reaction versus initial substrate concentration for both enzymes have a hyperbolic shape; the affinities of both enzymes for the substrate appear to be similar (Km = 20 mM). Both enzymes are inhibited by L-isoleucine, the shape of the kinetic plots being thereby changed into sigmoidal. Solubilization results in a decrease of the mitochondral enzyme sensitivity to the inhibition by L-isoleucine and in an appearance of cooperative interactions between the allosteric sites.

Hydrogen-Ion Concentration↗
PubMed1979

[Effect of higher alcohols on the activity of biosynthetic L-threonine dehydratase from Saccharomyces carlsbergensis brewer's yeast].

The effects of low (1 . 10(-4) M) and high (1 . 10(-3) M) concentrations of n-propanol, isobutanol and isoamylols on the kinetic behaviour of "biosynthetic" L-threonine dehydratase from brewer's yeast S. carlsbergensis 776 were studied. It was concluded that these alcohols control the activity of the first enzyme of the L-threonine biosynthetic pathway.

Alcohols↗
PubMed1979

[Kinetic patterns of their reactions catalyzed by membrane-bound monoamine oxidase].

The initial rate (v) versus initial substrate concentration [S]0 plots for the reaction of serotonin deamination catalyzed by rat liver mitochondrial monoamine oxidase are characterized by complicated non-hyperbolic patterns. The shapes of the curves in the plots depend on the age and strain of the animals used or on alterations in the physico-chemical state of mitochondria caused by freezing -- thawing and swelling in hypotonic solutions. The v versus [S]0 plots for other substrates (e. g. tyramine) do not obey the Michaelis -- Menten equation as well. In order to interpret the kinetic patterns described a model of the mitochondrial monoamine oxidase structure and function has been proposed. The model is based on the assumption that both catalytic and regulatory allosteric sites are present on the surface of monoamine oxidase molecules. In the process of serotonin or tyramine binding the monoamine oxidases exhibit cooperative properties which are characteristic for the allosteric enzymes. The model also suggests an active regulatory role of the mitochondrial membrane itself.

Animals↗
PubMed1978

[Interaction of intracellular RNAase from Aspergillus clavatus with derivatives of its substrates].

Using spectrophotometric and kinetic methods and also the methods of protection of Aspergillus clavatus RNAse (EC 3.1.4.23) by adenine nucleotides and their components against inactivation by means of acylation or heating, it was found that RNAse-nucleotide complex was formed by association of one enzyme molecule with one nucleotide molecule. It was also shown that all components of nucleotides (base, ribose and phosphate) take part in the formation of such complex and the removal of one of them (base or phosphate) lead to loosening of bindings of remaining fragments (ribose-5'-monophosphate, adenine) with the active site of RNAse, and to disappearance of bends within the pH range of 3.0-4.0 on the plot of pKi (5'-MP) versus pH, within the pH range of 5.5-7.0 on the plot of oKi (Ado) versus pH. The possibility of participation of associative pair RNAse imidasole groups - nucleotide phosphate groups and RNAse carboxylic group - nucleotide base in the mechanism of formation of enzyme-nucleotide (enzyme-substrate) complexes is postulated.

Acylation↗
PubMed1978

[Detection and properties of L-threonine-L-serine dehydratase in human liver].

It has been shown that in liver extract of men deceased by different causes, L-threonine and L-serine dehydratase activities probably, belonging to only one enzyme--L-threonine-L-serine dehydratase--are found. Both activities and their ratios depend on K+ concentration both in the buffer used for enzyme extraction and in the reaction medium. Before extraction of active and stable forms of enzyme the liver is to homogenized in a buffer containing 0.15 M KCl. Both enzymatic activities have a pH-optimum at pH 9.6--10.0. It was shown that D-isomers of threonine and serine are not dehydratated and do not inhibit dehydratation of L-isomers. Studies of dependence of L-threonine and L-serine dehydratase reaction rates on temperature showed that at any temperature ranges the energy activation values are higher for the L-threonine dehydratase reaction than for the L-serine dehydratase reaction and that the ratio reaction rates for both reactions depends on temperature.

Catalysis↗
PubMed1978

[Kinetics and thermodynamics of heat inactivation of L-threonine-L-serine dehydratase from human liver].

It has been shown that heat inactivation of L-threonine- and L-serine dehydratase activities at 37; 45; 50 and 55 degrees C in human liver extracts (the liver was ectracted with buffer containing 1.10(-5) M of pyridoxal 5'-phosphate) in course of time is practically identical, and characterizes by the same of values of activation energy of heat inactivation process, activation enthalpy of this process, activation free energy of that and activation enthalpy of the heat inactivation process. A rise of pyridoxal 5'-phosphate concentration (to 2.10(-4) M) in the buffer used for the liver extraction and hence in the medium in which the heat inactivation process was carried out stabilises L-threonine- and L-serine dehydratase activities against the inactivation at 55 degrees C. It has been concluded thatL-threonine- and L-serine dehydratase activities in human liver belong to the single protein or to two proteins having very like physico-chemical properties, and that pyridoxal 5'-phosphate is essential for this enzyme not only as coenzyme but also it is necessary to support active and stable conformation of this oligomeric protein.

Adult↗
PubMed1977

[Several kinetic features of membrane-dependent monoamine oxidase].

The v versus (S) plots for the initial rates of serotonin oxidation, catalyzed by monoamine oxidase in fragments of the rat liver or bovine brain mitochondrial membrane, had complicated non-hyperbolic shape, suggesting kinetic manifestation of cooperation in binding the substrate by the enzyme. A possibility of interactions of different monoamine oxidase types via the conformational alterations in the bio-membrane itself is considered.

Animals↗
PubMed1975

Studies of homogeneous "biosynthetic" L-threonine dehydratase from Escherichia coli K-12. Some kinetic properties and molecular multiplicity.

"Biosynthetic" L-threonine dehydratase (EC 4.2.1.16) was purified to a homogeneous state with 29% yield of total activity from Escherichia coli K-12. The homogeneity of the enzyme was shown by polyacrylamide gel disc electrophoresis in the presence of dodecyl sulphate. The enzyme consisted of equal subunits having a molecular weight of about 57 000. The polyacrylamide gel disc electrophoresis has shown that the native enzyme consisted of a set of oligomeric forms. The multiplicity of molecular organization of the enzyme was reflected in complicated kinetic behaviour: at pH greater than 9 on the plots of initial reaction rate (v) versus initial substrate concentration ([S]o) there were four inflexion points (two intermediate plateaux), the position and deepness of which depended on enzyme concentration. At pH 8.3 on the v versus [S]o plots appeared two inflexion points (one intermediate plateu), the position of which practically did not depend on enzyme concentration in the reaction mixture, but strongly depended on the enzyme concentration in the stock solution. Repeated polyacrylamide gel disc electrophoresis of several oligomeric forms, isolated by the first electrophoresis, has shown that the oligomeric forms underwent a slow polymerization. It was suggested that "biosynthetic" L-threonine dehydratase from E. coli K-12 is a set of multiple oligomeric forms, having different kinetic parameters. Probably, each form of the enzyme has a "simple" kinetics characterized by hyperbolic or sigmoidal shape of v versus [S]o plots. The rate of equilibrium installation between the oligomeric forms was small in comparison with the enzyme reaction velocity, that lead to the complex kinetic curves, appearing as a result of summing up of the kinetics inherent to theindividual forms.

Escherichia coli↗