scholarly journals Denaturation studies on natural and recombinant bovine prochymosin (prorennin)

1990 ◽  
Vol 271 (2) ◽  
pp. 541-547 ◽  
Author(s):  
R Sugrue ◽  
F A O Marston ◽  
P A Lowe ◽  
R B Freedman
Keyword(s):  
Inclusion Bodies ◽  
Kinetic Studies ◽  
Order Rate Constant ◽  
Slow Process ◽  
Equilibrium Studies ◽  
First Order ◽  
Denaturant Concentration ◽  
Recombinant Product ◽  
Stabilization Energies ◽  
Solubilization Of Inclusion Bodies

1. Prochymosin in solution in the presence of 8 M-urea is fully unfolded, as indicated by its fluorescence spectrum, fluorescence quenching behaviour and far-u.v.c.d. spectrum. 2. Equilibrium studies on the unfolding of prochymosin and pepsinogen by urea were carried out at pH 7.5 and pH 9.0. The results indicate that the stabilization energies of the two proteins are identical at pH 7.5, but that at pH 9.0 pepsinogen is significantly less stable than prochymosin. 3. Kinetic studies on the unfolding of prochymosin and pepsinogen indicate that the processes can be described by a single first-order rate constant, and that at any given value of denaturant concentration and pH the rate of unfolding of prochymosin is significantly greater than that of pepsinogen. 4. Unfolding of prochymosin by concentrated urea is not fully reversible, unlike that of pepsinogen. Kinetic analysis of the refolding of the proteins suggests the presence of a slow process following unfolding in urea; for pepsinogen this process leads to a slowly refolding form, whereas for prochymosin the slow process in urea leads to a form that cannot refold on dilution of the denaturant. 5. The results provide a rationale for an empirical process for recovery of recombinant prochymosin after solubilization of inclusion bodies in concentrated urea. 6. In all respects studied here, natural and recombinant bovine prochymosin were indistinguishable, indicating that the refolding protocol yields a recombinant product identical with natural prochymosin.

Kinetic Studies on Oxidation of Veratryl Alcohol by Laccase-Mediator System. Part 1. Effects of Mediator Concentration

Holzforschung ◽  
2000 ◽  
Vol 54 (2) ◽  
pp. 165-170 ◽  
Author(s):  
Mikhail Yu. Balakshin ◽  
Chen-Loung Chen ◽  
Josef S. Gratzl ◽  
Adrianna G. Kirkman ◽  
Harald Jakob
Keyword(s):  
Kinetic Studies ◽  
Veratryl Alcohol ◽  
Alcohol Oxidation ◽  
Order Rate Constant ◽  
Molar Ratio ◽  
Active Centers ◽  
First Order ◽  
System Part ◽  
Kinetics Of

Summary Kinetics of the laccase-catalyzed oxidation of veratryl alcohol with dioxygen in the presence of 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diamonium salt (ABTS), the mediator, were studied to elucidate the possible reaction mechanism and the role of the mediator in this reaction. The reaction follows a pseudo-first order reaction law. The first order rate constant (κ) is dependent on the Mediator/Substrate (M/S) ratio and has a maximum at M/S molar ratio of 0.15. The kinetic studies show that the mechanism of veratryl alcohol oxidation with dioxygen-laccase-ABTS is rather complex and includes different reaction pathways. The mediator is involved in competitive reactions. It has been suggested that at low mediator concentration, the veratryl alcohol is oxidized via the laccase redox cycle. The mediator acts mostly as a laccase activator at a M/S ratio lower than 0.15. With increasing ABTS concentration with respect to the substrate concentration, ABTS acts increasingly as a cosubstrate competing with the original substrate for active centers of the laccase. This results in inhibition of veratryl alcohol oxidation in the enzyme cycle and increases the role of substrate oxidation by an oxidized mediator.

scholarly journals Behaviour of Silica and Florisil as Solid Supports in the Removal Process of As(V) from Aqueous Solutions

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Andreea Gabor ◽  
Corneliu Mircea Davidescu ◽  
Adina Negrea ◽  
Mihaela Ciopec ◽  
Lavinia Lupa
Keyword(s):  
Crown Ether ◽  
Aqueous Solutions ◽  
Adsorption Process ◽  
Kinetic Studies ◽  
Solid Supports ◽  
Equilibrium Studies ◽  
First Order ◽  
Pseudo Second Order ◽  
Trace Concentrations ◽  
Solid Liquid

In this study two solid supports, silica and florisil, were impregnated with crown ether (dibenzo-18-crown-6) and Fe(III) ions and their efficiency was compared in the adsorption process of As(V) from aqueous solutions. The solid supports were impregnated with crown ether due to their ability to build complexes with positives ions. Fe(III) was used because of As(V) affinity for it. The impregnated solid supports were characterized by energy dispersive X-ray analysis, scanning electron microscopy, Fourier transform infrared spectroscopy, and the specific surface area. The influence of the solid : liquid ratio on the adsorption process, kinetic studies for the pseudo-first-order and pseudo-second-order, and activation energy were studied. Thermodynamic studies as well as equilibrium studies were carried out. The obtained results showed that, from the two considered materials, impregnated silica presents a higher efficiency with a good selectivity, able to remove As(V) from aqueous solutions containing trace concentrations.

Studies on sorption of cadmium (II) ions onto Haro river sand from aqueous media using radiotracer and voltammetric techniques

2006 ◽  
Vol 94 (8) ◽  
Author(s):  
Riaz Ahmed ◽  
Tayyaba Yamin ◽  
Muhammad S. Ansari ◽  
Syed Moosa Hasany
Keyword(s):  
Aqueous Media ◽  
Kinetic Studies ◽  
Order Rate Constant ◽  
River Sand ◽  
Radiotracer Technique ◽  
First Order ◽  
Ph Values ◽  
Voltammetric Techniques ◽  
Effects Of Ph ◽  
Intra Particle Diffusion

SummarySorption of Cd(II) ions on Haro river sand has been studied using radiotracer technique. The effects of pH and acid concentrations on the sorption were studied. The sorption increases with pH, reaches a maximum at pH7 and decreases at higher pH values. With acids, it was found that sorption decreases with increasing acid concentration, and for more oxidizing acids sorption was less. Kinetic studies indicate that mostly intra particle diffusion occurs with first order rate constant of 18.45 × 10

Reaction of alkaline sodium picrate with creatinine: I. Kinetics and mechanism of formation of the mono-creatinine picric acid complex.

1976 ◽  
Vol 22 (10) ◽  
pp. 1664-1671 ◽  
Author(s):  
J Vasiliades
Keyword(s):  
Picric Acid ◽  
Kinetic Studies ◽  
Order Rate Constant ◽  
Mechanism Of Formation ◽  
Creatinine Concentration ◽  
Acid Complex ◽  
First Order ◽  
Sodium Picrate ◽  
A Value ◽  
Complex Dependence

Abstract Spectrophotometric, kinetic, and nuclear magnetic resonance studies indicate that alkaline sodium picrate and creatinine react to form a 1/1 aduct between picric and creatinine, with a stability constant of log K= 4.26. Kinetic studies indicate that the forward reaction is first order with respect to picric acid, hydroxide, and creatinine concentration. The reverse reaction, the dissociation of the 1/1 complex, shows a complex dependence on hydroxide concentration. The expression for the observed pseudo-first-order rate constant in the presence of excess picric acid is: Kobsd = K1K0[P][OH] +[K2[OH]x. A value of K1K0 = 5.0 (mol/liter)-2s-1 is obtained. For accurate analytical results with this reaction, hydroxide concentration must be maintained at a constant value for both samples and standards.

scholarly journals Photoenzymatic Repair of Ultraviolet Damage in DNA

1962 ◽  
Vol 45 (4) ◽  
pp. 725-741 ◽  
Author(s):  
Claud S. Rupert
Keyword(s):  
Heavy Metals ◽  
Quantum Yield ◽  
Kinetic Studies ◽  
Order Rate Constant ◽  
Reaction Scheme ◽  
First Order ◽  
Substrate Complex ◽  
Enzyme Substrate ◽  
Exponential Decrease ◽  
Ultraviolet Damage

The photoenzyme from bakers' yeast which repairs ultraviolet-inactivated transforming DNA is mechanically bound to ultraviolet-irradiated DNA in the dark, but not to unirradiated DNA. In the bound condition it is stabilized against inactivation by heat and heavy metals. Both the mechanical binding and stabilization are eliminated by illumination. These observations are consistent with the reaction scheme suggested by kinetic studies, in which the enzyme combines with the ultraviolet lesions in DNA and the complex absorbs light, producing repair and subsequent liberation of the enzyme. The approximately exponential decrease of heat stabilization during illumination gives the first order rate constant for the light-dependent step at the corresponding light intensity. This quantity in turn sets limits on the possible magnitude of the molar absorption coefficient of the enzyme-substrate complex and on the quantum yield of the process.

scholarly journals Kinetic studies of the reduction of neutrophil cytochrome b-558 by dithionite

1986 ◽  
Vol 237 (2) ◽  
pp. 567-572 ◽  
Author(s):  
I Aviram ◽  
M Sharabani
Keyword(s):  
Cytochrome B ◽  
Rate Constant ◽  
Reaction Rate ◽  
Kinetic Studies ◽  
Order Rate Constant ◽  
First Order ◽  
Order Rate ◽  
Ionic Detergent ◽  
Activated Neutrophils ◽  
Membrane Bound

The reduction with dithionite of neutrophil cytochrome b-558, implicated in superoxide generation by activated neutrophils, was investigated by a stopped-flow technique in non-ionic-detergent extracts of the membranes and in crude membrane particles. The dependence of the pseudo-first-order rate constants on the concentration of dithionite was consistent with a mechanism of reduction that involves the dithionite anion monomer SO2.- as the reactive species. The estimated second-order rate constant was 7.8 × 10(6) M-1 × S-1 for Lubrol PX-solubilized cytochrome b-558 and 5.1 × 10(6) M-1 × S-1 for the membrane-bound protein. The similarity of the kinetic constants suggests that solubilization did not introduce gross changes in the reactive site. Imidazole and p-chloromercuribenzoate, known as inhibitors of NADPH oxidase, did not affect significantly cytochrome b-558 reduction rates. The reaction rate of cytochrome b-558 with dithionite exhibited a near-zero activation energy. The first-order rate constant for reduction decreased with increasing ionic strength, indicating a positive effective charge on the reacting protein.

The polymerization of ethylene on chromium oxide catalysts I. Kinetic studies

1972 ◽  
Vol 329 (1579) ◽  
pp. 361-373 ◽  
Keyword(s):  
Rate Constant ◽  
Initial Pressure ◽  
Kinetic Studies ◽  
Order Rate Constant ◽  
Polymerization Reaction ◽  
First Order ◽  
Ethylene Pressure ◽  
Order Rate ◽  
Chromium Vi ◽  
Chromium Oxide Catalysts

The rates of polymerization of ethylene on a supported chromium (VI) oxide Phillips catalysts have been measured. Catalysts were calcined in air at 460 °C and activated by pretreatment with ethylene at 300 °C. With increasing pretreatment times the activity of the catalyst increased to a maximum, after which over-reduction occurred and the activity fell. The products of the pretreatment process were water, carbon dioxide and a trace of butenes. Rates of polymerization were first order in ethylene pressure over the temperature range studied ( – 95 to 150 °C). The first order rate constant was sensitive to the initial pressure of ethylene added to the catalyst at the temperature at which the polymerization reaction was carried out. The results are explicable in terms of the production of active centres in the catalyst surface during contact with ethylene at 300 °C. Subsequent evacuation at 300 °C produced from some of these centres sites which had to be reactivated by adsorption of ethylene at low temperatures. The extent of re-activation increased with increasing ethylene pressure. The variation of first order rate constant with temperature showed a maximum at ca . – 23 °C and an apparent activation energy of 0.8 kJ mol -1 for the range –95 to – 23 °C. At temperatures above 227 °C the rate of polymerization was extremely slow.

Development of Sustained Release Multi-Component Microparticulate System of Diclofenac Sodium and Tizanidine Hydrochloride

1970 ◽  
Vol 1 (1) ◽  
pp. 97-105
Author(s):  
Kamlesh Dashora ◽  
Shailendra Saraf ◽  
Swarnalata Saraf
Keyword(s):  
Particle Size ◽  
Sustained Release ◽  
Cellulose Acetate ◽  
Rate Constant ◽  
Diclofenac Sodium ◽  
Order Rate Constant ◽  
Anomalous Transport ◽  
First Order ◽  
Sem Study ◽  
Transport Type

Sustained released tablets of diclofenac sodium (DIC) and tizanidine hydrochloride (TIZ) were prepared by using different proportions of cellulose acetate (CA) as the retardant material. Nine formulations of tablets having different proportion of microparticles developed by varied proportions of polymer: drug ratio ‘’i.e.’’; 1:9 -1:3 for DIC and 1:1 – 3:1 for TIZ. Each tablet contained equivalent to 100 mg of DIC and 6mg of TIZ. The prepared microparticles were white, free flowing and spherical in shape (SEM study), with  the particle size varying from 78.8±1.94 to 103.33±1.28 µm and 175.92± 9.82 to 194.94±14.28µm for DIC  and TIZ, respectively.  The first order rate constant K1 of formulations were found to be in the range of  K1 = 0.117-0.272 and 0.083- 0.189 %hr-1for DIC and TIZ, respectively. The value of exponent coefficient (n) was found to be in the range of 0.6328-0.9412  and 0.8589-1.1954 for DIC and TIZ respectively indicates anomalous  to  non anomalous transport type of diffusions among different formulations

Kinetic Studies of [4n+2]π-Thermal Cyclodimerization of 1-(3-Pyridazinyl)-3-oxidopyridinium Betaines

1992 ◽  
Vol 57 (9) ◽  
pp. 1951-1959 ◽  
Author(s):  
Madlene L. Iskander ◽  
Samia A. El-Abbady ◽  
Alyaa A. Shalaby ◽  
Ahmed H. Moustafa
Keyword(s):  
Energy Gap ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Cyclic Transition ◽  
Concerted Mechanism ◽  
First Order ◽  
Thermodynamic Activation Parameters ◽  
Cyclic Transition State ◽  
Complete Dissociation ◽  
Homo Lumo

The reactivity of the base induced cyclodimerization of 1-(6-arylpyridazin-3-yl)-3-oxidopyridinium chlorides in a pericyclic process have been investigated kinetically at λ 380 nm. The reaction was found to be second order with respect to the liberated betaine and zero order with respect to the base. On the other hand dedimerization (monomer formation) was found to be first order. It was shown that dimerization is favoured at low temperature, whereas dedimerization process is favoured at relatively high temperature (ca 70 °C). Solvent effects on the reaction rate have been found to follow the order ethanol > chloroform ≈ 1,2-dichloroethane. Complete dissociation was accomplished only in 1,2-dichloroethane at ca 70 °C. The thermodynamic activation parameters have been calculated by a standard method. Thus, ∆G# has been found to be independent on substituents and solvents. The high negative values of ∆S# supports the cyclic transition state which is in favour with the concerted mechanism. MO calculations using SCF-PPP approximation method indicated low HOMO-LUMO energy gap of the investigated betaines.

Adsorptive Removal of Cd(II) by a Novel Extracellular Biopolymer Produced by Pseudomonas alcaligenes: Equilibrium and Kinetics

2010 ◽  
Vol 171-172 ◽  
pp. 15-18
Author(s):  
Zeng Quan Ji ◽  
Tian Hai Wang ◽  
Kai Hong Luo ◽  
Yao Qing Wang
Keyword(s):  
Chemical Interaction ◽  
Kinetic Studies ◽  
Maximum Adsorption Capacity ◽  
Metallic Ions ◽  
Equilibrium Studies ◽  
Kinetic Rates ◽  
Equilibrium And Kinetics ◽  
Potential Applications ◽  
Pseudo Second Order ◽  
Pseudomonas Alcaligenes

An extracellular biopolymer (PFC02) produced by Pseudomonas alcaligenes was used as an alternative biosorbent to remove toxic Cd(II) metallic ions from aqueous solutions. The effect of experimental parameters such as pH, Cd(II) initial concentration and contact time on the adsorption was studied. It was found that pH played a major role in the adsorption process, the optimum pH for the removal of Cd(II) was 6.0. The FTIR spectra showed carboxyl, hydroxyl and amino groups of the PFC02 were involved in chemical interaction with the Cd(II) ions. Equilibrium studies showed that Cd(II) adsorption data followed Langmuir model. The maximum adsorption capacity (qmax) for Cd(II) ions was estimated to be 93.55 mg/g. The kinetic studies showed that the kinetic rates were best fitted to the pseudo-second-order model. The study suggestted that the novel extracellular biopolymer biosorbent have potential applications for removing Cd(II) from wastewater.

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