Determination of the rate-limiting steps for malic enzyme by the use of isotope effects and other kinetic studies

Biochemistry ◽  
1977 ◽  
Vol 16 (4) ◽  
pp. 571-576 ◽  
Author(s):  
Michael I. Schimerlik ◽  
C. E. Grimshaw ◽  
W. W. Cleland
Keyword(s):  
Malic Enzyme ◽  
Isotope Effects ◽  
Kinetic Studies ◽  
Rate Limiting

Determination of the Chemical Mechanism of Malic Enzyme by Isotope Effects†

Biochemistry ◽  
1997 ◽  
Vol 36 (5) ◽  
pp. 1141-1147 ◽  
Author(s):  
William A. Edens ◽  
Jeffrey L. Urbauer ◽  
W. W. Cleland
Keyword(s):  
Malic Enzyme ◽  
Isotope Effects ◽  
Chemical Mechanism

scholarly journals Kinetics and mechanism of the anilinolysis of aryl phenyl isothiocyanophosphates in acetonitrile

2013 ◽  
Vol 9 ◽  
pp. 615-620 ◽  
Author(s):  
Hasi Rani Barai ◽  
Hai Whang Lee
Keyword(s):  
Isotope Effects ◽  
Bond Formation ◽  
Kinetic Studies ◽  
Kinetic Isotope Effects ◽  
Bond Breaking ◽  
Stepwise Mechanism ◽  
Kinetic Isotope ◽  
Energy Relationships ◽  
Break Region ◽  
Rate Limiting

Kinetic studies on the reactions of Y-aryl phenyl isothiocyanophosphates with substituted X-anilines and deuterated X-anilines were carried out in acetonitrile at 55.0 °C. The free-energy relationships with X in the nucleophiles were biphasic concave upwards with a break region between X = H and 4-Cl, giving unusual positive ρX and negative βX values with less basic anilines (X = 4-Cl and 3-Cl). A stepwise mechanism with rate-limiting bond breaking for more basic anilines and with rate-limiting bond formation for less basic anilines is proposed based on the positive and negative ρXY values, respectively. The deuterium kinetic isotope effects involving deuterated anilines (XC6H4ND2) showed primary normal and secondary inverse DKIEs for more basic and less basic anilines, rationalized by frontside attack involving hydrogen-bonded four-center-type TSf and backside attack TSb, respectively. The positive ρX values with less basic anilines are substantiated by the tight TS, in which the extent of the bond formation is great and the degree of the bond breaking is considerably small.

Determination of the Mechanism of Human Malic Enzyme with Natural and Alternate Dinucleotides by Isotope Effects

2001 ◽  
Vol 396 (1) ◽  
pp. 43-48 ◽  
Author(s):  
Mark A. Rishavy ◽  
Zhiru Yang ◽  
Liang Tong ◽  
W.W. Cleland
Keyword(s):  
Malic Enzyme ◽  
Isotope Effects

Stability Indicating Liquid Chromatographic Method for the Determination of Fenofibrate and its Application to Kinetic Studies

2013 ◽  
Vol 5 (4) ◽  
pp. 1866-1874
Author(s):  
K. Srinivasa Rao ◽  
Keshar N K ◽  
N Jena ◽  
M.E.B Rao ◽  
A K Patnaik
Keyword(s):  
Degradation Products ◽  
Kinetic Studies ◽  
Pharmaceutical Formulations ◽  
Assay Method ◽  
Pharmaceutical Dosage Form ◽  
Stability Indicating ◽  
Zero Order Kinetics ◽  
Relative Standard ◽  
Liquid Chromatographic

A stability-indicating LC assay method was developed for the quantitative determination of fenofibrate (FFB) in pharmaceutical dosage form in the presence of its degradation products and kinetic determinations were evaluated in acidic, alkaline and peroxide degradation conditions. Chromatographic separation was achieved by use of Zorbax C18 column (250 × 4.0 mm, 5 μm). The mobile phase was established by mixing phosphate buffer (pH adjusted 3 with phosphoric acid) and acetonitrile (30:70 v/v). FFB degraded in acidic, alkaline and hydrogen peroxide conditions, while it was more stable in thermal and photolytic conditions. The described method was linear over a range of 1.0-500 μg/ml for determination of FFB (r= 0.9999). The precision was demonstrated by relative standard deviation (RSD) of intra-day (RSD= 0.56– 0.91) and inter-day studies (RSD= 1.47). The mean recovery was found to be 100.01%. The acid and alkaline degradations of FFB in 1M HCl and 1M NaOH solutions showed an apparent zero-order kinetics with rate constants 0.0736 and 0.0698  min−1 respectively and the peroxide degradation with 5% H2O2 demonstrated an apparent first-order kinetics with rate constant k = 0.0202 per min. The t1/2, t90   values are also determined for all the kinetic studies. The developed method was found to be simple, specific, robust, linear, precise, and accurate for the determination of FFB in pharmaceutical formulations.  

scholarly journals Lifetime predictions of non-ionic and ionic biopolymers: kinetic studies by non-isothermal thermogravimetric analysis

2021 ◽  
Author(s):  
Martina Maria Calvino ◽  
Lorenzo Lisuzzo ◽  
Giuseppe Cavallaro ◽  
Giuseppe Lazzara ◽  
Stefana Milioto
Keyword(s):  
Degradation Kinetics ◽  
Kinetic Studies ◽  
Ionic Polymers ◽  
Heating Rates ◽  
Exponential Factor ◽  
Master Plot ◽  
Plot Analysis ◽  
Sustainable Polymers ◽  
Master Plot Analysis

AbstractIn this paper, films based on sustainable polymers with variable charge have been investigated by non-isothermal thermogravimetry in order to predict their lifetime, which is a key parameter for their potential use in numerous technological and biomedical applications. Specifically, chitosan has been selected as positively charged biopolymer, while alginate has been chosen as negatively charged biopolymer. Among non-ionic polymers, methylcellulose has been investigated. Thermogravimetric measurements at variable heating rates (5, 10, 15 and 20 °C min−1) have been performed for all the polymers to study their degradation kinetics by using isoconversional procedures combined with ‘Master plot’ analyses. Both integral (KAS and Starink methods) and differential (Friedman method) isoconversional procedures have shown that chitosan possesses the highest energetic barrier to decomposition. Based on the Master plot analysis, the decomposition of ionic polymers can be described by the R2 kinetic model (contracted cylindrical geometry), while the degradation of methylcellulose reflects the D2 mechanism (two-dimensional diffusion). The determination of both the decomposition mechanism and the kinetic parameters (activation energy and pre-exponential factor) has been used to determine the decay time functions of the several biopolymers. The obtained insights can be helpful for the development of durable films based on sustainable polymers with variable electrostatic characteristics. Graphical abstract

Inhibition of carbon fixation as a function of zinc uptake in natural phytoplankton assemblages

1979 ◽  
Vol 59 (4) ◽  
pp. 937-949 ◽  
Author(s):  
Anthony G. Davies ◽  
Jillian A. Sleep
Keyword(s):  
Carbon Fixation ◽  
Natural Populations ◽  
Plant Cells ◽  
Toxic Metal ◽  
Vitamin B ◽  
Phytoplankton Assemblages ◽  
Metal Contents ◽  
Rate Limiting ◽  
Natural Phytoplankton

There is now a substantial body of evidence that the growth rates of phytoplankton in culture are more closely related to the cellular levels of the rate-limiting constituent, be it a nutrient, micronutrient or toxic metal, than to the concentrations in the supporting medium; nitrate, Caperon (1968); phosphate, Fuhs (1969); silicate, Paasche (1973); vitamin B12, Droop (1968); iron, Davies (1970); mercury, Davies (1974); cadmium, Davies (1978a). This has suggested the requirement for a technique which would allow the determination of comparable relationships for natural populations of phytoplankton - how, for instance, their carbon fixation rates depend upon the metal contents of the plant cells. Although the effects of metals upon carbon fixation in phytoplankton assemblages from several different sea areas have already been examined (Knauer & Martin, 1972; Patin et al. 1974; Zingmark & Miller, 1975; Ibragim & Patin, 1976) no data seem to have been obtained on the levels of the metals present in the phytoplankton at the time of the measurements.

Removal of Mg from spring water using natural clinoptilolite

Clay Minerals ◽  
2012 ◽  
Vol 47 (1) ◽  
pp. 81-92 ◽  
Author(s):  
S. Tomić ◽  
N. Rajić ◽  
J. Hrenović ◽  
D. Povrenović
Keyword(s):  
Ion Exchange ◽  
Kinetic Studies ◽  
Spring Water ◽  
Zeolite A ◽  
Zeolitic Tuff ◽  
Rate Limiting Step ◽  
Intra Particle Diffusion ◽  
Pseudo Second Order ◽  
Natural Clinoptilolite ◽  
Rate Limiting

AbstractNatural zeolitic tuff from Brus (Serbia) consisting mostly of clinoptilolite (about 90%) has been investigated for the reduction of the Mg concentration in spring water. The sorption capacity of the zeolite is relatively low (about 2.5 mg Mg g-1for the initial concentration of 100 mg Mg dm-3). The zeolitic tuff removes Mg from water solutions by ion exchange, which has been demonstrated by energy dispersive X-ray analysis (EDS). The extent of ion exchange was influenced by the pH and the initial Mg concentration. Kinetic studies revealed that Lagergen's pseudo-second order model was followed. Intra-particle diffusion of Mg2+influenced the ion exchange, but it is not the rate-limiting step. Rather than having to dispose of the Mg-loaded (waste) zeolite, a possible application was tested. Addition to a wastewater with a low concentration of Mg showed that it could successfully make up for the lack of Mg micronutrient and, accordingly, enabled the growth of phosphate-accumulating bacteriaA. Junii, increasing the amount of phosphate removed from the wastewater.

scholarly journals Micellar Electrokinetic Chromatographic Study of the Separation of an Aromatase Inhibitor and a Tryciclic Antidepressant in the Breast Cancer Treatment

2008 ◽  
Vol 3 ◽  
pp. ACI.S939 ◽  
Author(s):  
J. Rodríguez Flores ◽  
A.M. Contento Salcedo ◽  
L. Muñoz Fernández
Keyword(s):  
Micellar Electrokinetic Chromatography ◽  
Solid Phase ◽  
Background Electrolyte ◽  
Kinetic Studies ◽  
Breast Cancer Treatment ◽  
Chromatographic Study ◽  
Optimal Conditions ◽  
Sodium Dodecylsulphate ◽  
Experimental Parameters

Micellar electrokinetic chromatography (MEKC) was investigated for the simultaneous determination of letrozole, imipramine and their metabolites in human urine samples over a concentration range of therapeutic interest. Experimental parameters such as pH of the running electrolyte, sodium dodecylsulphate (SDS) concentration, borate concentration, voltage, etc were investigated. Under optimal conditions of 25 mM SDS, 15 mM borate buffer (pH 9.2), 15% 2-propanol, as background electrolyte; 28 kV and 40 °C, as voltage and cartridge temperature, respectively; resolution between the peaks was greater than 1.7. Before the determination, a solid phase extraction (SPE) procedure with a C18 cartridge was optimized. Good linearity, accuracy, precision, robustness and ruggedness were achieved and detection limits of 12.5 ng/mL for letrozole and its metabolite and 37.5 ng/mL, were obtained for imipramine and their metabolites. Real determinations of these analytes in two patient urines were carried out. Sensitivity achieved in this method is sufficient to perform kinetic studies in humans.

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