scholarly journals Kinetics of protein-modification reactions. Determination of the fractional concentration of enzyme protein groups, or group reactivities, essential for catalytic function

1986 ◽  
Vol 237 (2) ◽  
pp. 589-591 ◽  
Author(s):  
E T Rakitzis ◽  
T B Malliopoulou
Keyword(s):  
Protein Modification ◽  
Initial Reaction ◽  
Mathematical Treatment ◽  
Enzyme Protein ◽  
First Derivative ◽  
Catalytic Function ◽  
Fractional Concentration ◽  
Reactive Groups ◽  
Activity Loss

A mathematical treatment of modification-induced enzyme protein inactivation is presented, and it is shown that, at initial reaction conditions, the ratio of the first derivative of the equation describing enzyme activity loss to the first derivative of the equation describing protein groups modification is equal to the fractional concentration of enzyme protein reactive groups, or group reactivities, essential for catalytic function.

scholarly journals Kinetics of protein-modification reactions. Stoichiometry of modification-produced enzyme inactivation: modification of rhodanese by 2,4,6-trinitrobenzenesulphonic acid

1985 ◽  
Vol 230 (1) ◽  
pp. 89-93 ◽  
Author(s):  
E T Rakitzis ◽  
T B Malliopoulou
Keyword(s):  
Protein Modification ◽  
Reaction Medium ◽  
Enzyme Inactivation ◽  
Mathematical Treatment ◽  
Modifying Agent ◽  
Catalytic Function ◽  
Reactive Groups ◽  
Decreasing Ph ◽  
Activity Loss ◽  
Kinetics Of

A mathematical treatment is presented for the dependence of enzyme activity loss on the numbers and reactivities of the groups essential for catalytic function, when enzyme protein modification is carried out by the use of concentrations of protein reactive groups well in excess of that of modifying agent. Experimentally obtained data on the modification of rhodanese (thiosulphate sulphurtransferase, EC 2.8.1.1) by 2,4,6-trinitrobenzenesulphonic acid are presented, and it is shown that, at pH9.00, the fractional concentration of rhodanese groups, or of rhodanese group reactivities, essential for enzyme catalytic function is 0.88; this value is found to decrease with decreasing pH of the reaction medium. The possibility that rhodanese inactivation by 2,4,6-trinitrobenzenesulphonic acid is brought about by modification of groups other than amino groups is ruled out by a comparison of the enzyme-inactivation and protein-modification stoichiometries, for putative reaction models for enzyme and modifying agent.

scholarly journals Three Different Spectrophotometric Methods for Simultaneous Determination of Pyriproxyfen and Chlorothalonil Residues in Cucumber and Cabbage Samples

2019 ◽  
Vol 2019 ◽  
pp. 1-11
Author(s):  
Shilan A. Omer ◽  
Nabil A. Fakhre
Keyword(s):  
Simultaneous Determination ◽  
Simultaneous Estimation ◽  
Zero Crossing ◽  
Spectrophotometric Methods ◽  
First Derivative ◽  
The Third ◽  
Mean Centering ◽  
Relative Standard ◽  
One Way Anova

In this study, three simple and accurate spectrophotometric methods for simultaneous determination of pyriproxyfen and chlorothalonil residues in cucumbers and cabbages grown in experimental greenhouse were studied. The first method was based on the zero-crossing technique measurement for first and second derivative spectrophotometry. The second method was based on the first derivative of the ratio spectra. However, the third method was based on mean centering of ratio spectra. These procedures lack any previous separation steps. The calibration curves for three spectrophotometric methods are linear in the concentration range of 1–30 μg·mL−1 and 0.5–7 μg·mL−1 for pyriproxyfen and chlorothalonil successively. The recoveries ranged from 82.12–97.40% for pyriproxyfen and 81.51–97.04% for chlorothalonil with relative standard deviations less than 4.95% and 5.45% in all instances for pyriproxyfen and chlorothalonil, respectively. The results obtained from the proposed methods were compared statistically by using one-way ANOVA, and the results revealed there were no significant differences between ratio spectra and mean centering methods with the zero-crossing technique. The proposed methods are successfully applied for the simultaneous estimation of the residue of both pesticides in cucumber and cabbage samples.

scholarly journals Simultaneous Determination of Amlodipine and Valsartan

2011 ◽  
Vol 6 ◽  
pp. ACI.S7282 ◽  
Author(s):  
Nashwah Gadallah Mohamed
Keyword(s):  
Absorption Spectrum ◽  
Simultaneous Determination ◽  
Zero Order ◽  
Uv Spectrophotometry ◽  
Ratio Spectrum ◽  
First Derivative ◽  
Bulk Powder ◽  
Overlapped Peaks ◽  
Third Derivative

A spectrophotometric method was developed for simultaneous determination of amlodipine (Aml) and valsartan (Val) without previous separation. In this method amlodipine in methanolic solution was determined using zero order UV spectrophotometry by measuring its absorbency at 360.5 nm without any interference from valsartan. Valsartan spectrum in zero order is totally overlapped with that of amlodipine. First, second and third derivative could not resolve the overlapped peaks. The first derivative of the ratio spectra technique was applied for the measurement of valsartan. The ratio spectrum was obtained by dividing the absorption spectrum of the mixture by that of amlodipine, so that the concentration of valsartan could be determined from the first derivative of the ratio spectrum at 290 nm. Quantification limits of amlodipine and valsartan were 10-80 μg/ml and 20-180 μg/ml respectively. The method was successfully applied for the quantitative determination of both drugs in bulk powder and pharmaceutical formulation.

Spectrophotometric and first-derivative spectrophotometric determination of cadmium witho-hydroxybenzenediazoaminoazobenzene (HDAA)

1989 ◽  
Vol 97 (5-6) ◽  
pp. 313-320 ◽  
Author(s):  
Chung-Gin Hsu ◽  
Wei Wang ◽  
Li-Ping Yang ◽  
Jiao-Mai Pan ◽  
Yu-Fang Wang
Keyword(s):  
Spectrophotometric Determination ◽  
First Derivative
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