Wyniki wyszukiwania

1

An easy procedure to transform the ratio of two polynomials of first degree into Michaelis-Menten-type equations. Application to the ordered Uni Bi enzyme mechanism

100%

Fontes R., Ribeiro J. M., Sillero A.

Acta Biochimica Polonica

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2000

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tom 47

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nr 1

It is not always clear that some equations affected by complicated factors can, actually, be interpreted as a ratio of two polynomials of first degree and so that they can be, in general, represented by rectangular hyperbolas. In this paper we present an easy procedure to rearrange those equations into Michaelis-Menten-type equations and so to make the aspects of these rectangular hyperbolas more clear, particularly for researchers familiar with general biochemistry. As an example, the method is applied to transform the classical rate equation of the Cleland's Ordered Uni Bi enzyme mechanism.

2

Continuous assay for acid phosphatase using 1-naphthyl phosphate as a substrate

88%

Luchter-Wasylewska E.

Acta Biochimica Polonica

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1997

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tom 44

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nr 4

The described continuous acid phosphatase assay is based on kinetics of the release of 1-naphthol in the course of the enzyme-catalyzed hydrolysis of 1-naphthyl phosphate, measured at 320 nm in aqueous solution and at 322 nm in sodium-bis(2-ethylhexyl)sulfosuccinate isooctane-water reverse micelles in a broad pH range (1.0-8.2). The method allows precise determination of the initial rate of the reaction and therefore may be used in the steady-state and pre-steady-state studies on the phosphatase-catalyzed reaction. The kinetic parameters (Km and kcat) for human prostatic acid phosphatase in aqueous solution and in reverse micelles, at pH 3.8, 4.5 and 5.7, by the proposed 1-naphthyl phosphate assay have been determined.

3

Contribution of the intra- and intermolecular routes in autocatalytic zymogen activation: application to pepsinogen activation

75%

Varon R., Fuentes M. E., Garcia-Moreno M., Garcia-Sevilla F., Arias E., Valero E., Arribas E.

Acta Biochimica Polonica

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2006

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tom 53

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nr 2

Taking as the starting point a recently suggested reaction scheme for zymogen activation involving intra- and intermolecular routes and the enzyme-zymogen complex, we carry out a complete analysis of the relative contribution of both routes in the process. This analysis suggests the definition of new dimensionless parameters allowing the elaboration, from the values of the rate constants and initial conditions, of the time course of the contribution of the two routes. The procedure mentioned above related to a concrete reaction scheme is extrapolated to any other model of autocatalytic zymogen activation involving intra- and intermolecular routes. Finally, we discuss the contribution of both of the activating routes in pepsinogen activation into pepsin using the values of the kinetic parameters given in the literature.

4

The nonallosteric mechanism of enzyme activity regulation. Is it the only true mechanism

75%

Kuczek M.

Cellular and Molecular Biology Letters

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2003

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tom 08

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nr 1

The nonallosteric regulation mechanism of enzyme reaction velocity assumes that the substrate and enzyme interact via a metal cation and form simple and mixed, mono- and multi-nuclear complexes. A solution of equations for individual cases gives a function of initial reaction velocity at any given substrate or modifier concentration. This function can describe kinetic effects that are considered allosteric, as well as phenomena omitted by commonly-accepted models.

5

Transformation of dimeric low-affinity form of human thymidine kinase [TK1] to the tetrameric high-affinity form [ATP-form]

75%

Zuberek J., Munch-Petersen B., Shugar D., Kierdaszuk B.

Cellular and Molecular Biology Letters

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1999

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tom 04

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nr 3

6

Effect of sex and localization dependent differences of Na,K-ATPase properties in brain of rats

63%

Kolocayova B., Vrbjar N.

Journal of Physiology and Pharmacology

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2020

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tom 71

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nr 2

7

Binding of SPXK- and APXK-peptide motifs to At-rich DNA. Experimental and theoretical studies

63%

Brzeski J., Grycuk T., Lipkowski A. W., Rudnicki W., Lesyng B., Jerzmanowski A.

Acta Biochimica Polonica

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1998

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tom 45

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nr 1

The binding properties of the SPXK- and APXK-type peptides to the AT-rich DNA fragments of different length were studied by measuring the competition of peptides with Hoechst 33258 dye for DNA binding and by the gel shift assay analysis. In parallel to the experimental studies, molecular modeling techniques were used to analyze possible binding modes of the SPXZ and APXK motifs to the AT-rich DNA. The results of the competition measurements and gel shift assays suggest that serine at the i-1 position (i is proline) can be replaced by alanine without affecting the binding properties of the motif. Thus, the presence of the conserved serine in this motif in many DNA-binding proteins is probably not dictated by structural requirements. Based on the results of molecular modeling studies we propose that the binding mode of the SPXK- type motifs to the AT-rich DNA resembles closely that between the N-terminal arm of the homeodomain and DNA. This model confirms that serine in the SPXK motifs is not essential for the DNA binding. The model also indicates that if X in the motif is glutamic acid, this residue is probably protonated in the complex with DNA.

8

Inhibition and activation of enzymes. The effect of a modifier on the reaction rate and on kinetic parameters

63%

Fontes R., Ribeiro J. M., Sillero A.

Acta Biochimica Polonica

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2000

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tom 47

|

nr 1

A combined analysis of enzyme inhibition and activation is presented, based on a rapid equilibrium model assumption in which one molecule of enzyme binds one molecule of substrate (S) and/or one molecule of a modifier X. The modifier acts as activator (essential or non-essential), as inhibitor (total or partial), or has no effect on the reaction rate (v), depending on the values of the equilibrium constants, the rate constants of the limiting velocity steps, and the concentration of substrate ([S]). Different possibilities have been analyzed from an equation written to emphasize that v=([X]) is, in general and at a fixed [S], a hyperbolic function. Formulas for Su (the value of [S], different from zero, at which v is unaffected by the modifier) and vsu (v at that particular [S]) were deduced. In Lineweaver-Burk plots, the straight lines related to different [X] generally cross in a point (P) with coordinates (Su, vsu). In certain cases, point P is located in the first quadrant which implies that X acts as activator, as inhibitor, or has no effect, depending on [S]. Furthermore, we discuss: (1) the apparent Vmax and Km displayed by the enzyme in different situations; (2) the degree of effect (inhibition or activation) observed at different concentrations of substrate and modifier; (3) the concept of Ke, a parameter that depends on the concentration of substrate and helps to evaluate the effect of the modifier: it equals the value of [X] at which the increase or decrease in the reaction rate is half of that achieved at saturating [X]. Equations were deduced for the general case and for particular situations, and used to obtain computer-drawn graphs that are presented and discussed. Formulas for apparent Vmax, Km and Ke have been written in a way making it evident that these parameters can be expressed as pondered means

9

Kinetic analysis of the transient phase and steady state of open multicyclic enzyme cascades

63%

Varon R., Havsteen B. H., Valero E., Molina-Alarcon M., Garcia-Canovas F., Garcia-Moreno M.

Acta Biochimica Polonica

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2005

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tom 52

|

nr 4

This paper presents a kinetic analysis of the whole reaction course, i.e. of both the transient phase and the steady state, of open multicyclic enzyme cascade systems. Equations for fractional modifications are obtained which are valid for the whole reaction course. The steady state expressions for the fractional modifications were derived from the latter equations since they are not restricted to the condition of rapid equilibrium. Finally, the validity of our results is discussed and tested by numerical integration. Apart from the intrinsic value of knowing the kinetic behaviour of any of the species involved in any open multicyclic enzyme cascade, the kinetic analysis presented here can be the basis of future contributions concerning open multicyclic enzyme cascades which require the knowledge of their time course equations (e.g. evaluation of the time needed to reach the steady state, suggestion of kinetic data analysis, etc.), analogous to those already carried out for open bicyclic cascades.

10

Localization dependent sensitivity of cerebral Na,K-ATPase to irradiation induced oxidative imbalance in rats

51%

Kolocayova B., Kovacicova I., Radosinska J., Tothova L., Fulop M., Slezak J., Vrbjar N.

Journal of Physiology and Pharmacology

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2019

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tom 70

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nr 4

11

Cultivar variation in heat stability and kinetic properties of soluble invertase in wheat grains

51%

Asthir B., Kaur A., Basra A. S.

Acta Physiologiae Plantarum

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1998

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tom 20

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nr 4

Soluble invertase from mid-milky stage grains of two wheat (Triticum aestivum L.) varieties, namely Kalyansona and PBW 343 was isolated and purified by employing ammonium sulphate precipitation, gel filtration on Sephadex G-150 and DEAE-cellulose column chromatography. Invertase from Kalyansona exhibited greater heat stability (50 °C) compared to PBW 343 (35 °C). By employing photo-oxidation and chemical modification methods, and by studying the effect of pH on Km and Vmax, the involvement of histidine, sulphydryl and α-carboxyl groups in the active site of the enzyme was indicated. The enzyme was completely inhibited by HgCl₂ and DTNB. ZnSO₄, MgSO₄, KCl, CaCl₂, EDTA and pyridoxine were strong inhibitors in PBW 343 but not in Kalyansona. The two varieties also showed differential response in respect to thermodynamic properties of the enzyme, i.e. energy of activation (Ea), enthalpy change (ΔH) and entropy change (ΔS). Overall the results suggest that genetic differences exist in soluble invertase properties of wheat grains and that the thermal adaptation of the enzyme is reflected in its altered kinetic behaviour.

Ograniczanie wyników

An easy procedure to transform the ratio of two polynomials of first degree into Michaelis-Menten-type equations. Application to the ordered Uni Bi enzyme mechanism

Continuous assay for acid phosphatase using 1-naphthyl phosphate as a substrate

Contribution of the intra- and intermolecular routes in autocatalytic zymogen activation: application to pepsinogen activation

The nonallosteric mechanism of enzyme activity regulation. Is it the only true mechanism

Transformation of dimeric low-affinity form of human thymidine kinase [TK1] to the tetrameric high-affinity form [ATP-form]

Effect of sex and localization dependent differences of Na,K-ATPase properties in brain of rats

Binding of SPXK- and APXK-peptide motifs to At-rich DNA. Experimental and theoretical studies

Inhibition and activation of enzymes. The effect of a modifier on the reaction rate and on kinetic parameters

Kinetic analysis of the transient phase and steady state of open multicyclic enzyme cascades

Localization dependent sensitivity of cerebral Na,K-ATPase to irradiation induced oxidative imbalance in rats

Cultivar variation in heat stability and kinetic properties of soluble invertase in wheat grains