scholarly journals Kinetics of the course of inactivation of aminoacylase by 1,10-phenanthroline

1992 ◽  
Vol 281 (1) ◽  
pp. 285-290 ◽  
Author(s):  
Z X Wang ◽  
H B Wu ◽  
X C Wang ◽  
H M Zhou ◽  
C L Tsou
Keyword(s):  
Enzyme Activity ◽  
Active Site ◽  
Inactivation Kinetics ◽  
Slow Inactivation ◽  
Phenanthroline Complex ◽  
Rapid Reaction ◽  
Kinetics Of ◽  
Active Site Conformation ◽  
Inhibited Enzyme ◽  
Substrate Competition

The kinetic theory of the substrate reaction during modification of enzyme activity previously described [Tsou (1988) Adv. Enzymol. Relat. Areas Mol. Biol. 61, 381-436] has been applied to a study on the kinetics of the course of inactivation of aminoacylase by 1,10-phenanthroline. Upon dilution of the enzyme that had been incubated with 1,10-phenanthroline into the reaction mixture, the activity of the inhibited enzyme gradually increased, indicating dissociation of a reversible enzyme–1,10-phenanthroline complex. The kinetics of the substrate reaction with different concentrations of the substrate chloroacetyl-L-alanine and the inactivator suggest a complexing mechanism for inactivation by, and substrate competition with, 1,10-phenanthroline at the active site. The inactivation kinetics are single phasic, showing that the initial formation of an enzyme-Zn(2+)-1,10-phenanthroline complex is a relatively rapid reaction, followed by a slow inactivation step that probably involves a conformational change of the enzyme. The presence of Zn2+ apparently stabilizes an active-site conformation required for enzyme activity.

scholarly journals Kinetics of protein modification reactions. Plot of fractional enzyme activity versus extent of protein modification in cases where all modifiable groups are essential for enzyme activity

1984 ◽  
Vol 223 (1) ◽  
pp. 259-262 ◽  
Author(s):  
E T Rakitzis
Keyword(s):  
Enzyme Activity ◽  
Active Site ◽  
Protein Modification ◽  
Enzyme Molecule ◽  
Single Group ◽  
Initial Portion ◽  
Enzyme Active Site ◽  
Kinetics Of

The plot of fractional enzyme activity versus extent of protein modification, for cases where all enzyme modifiable groups of a certain kind are essential for activity, is found to be nearly independent of the number, per enzyme active site, of modifiable groups involved. Such plots usually, by a fallacious extension of the initial portion of the plot on the extent-of-modification axis, are interpreted to mean the modification of one single group per enzyme active site (or per enzyme molecule). The possible relevance of these findings to cases in the literature is discussed.

Thermal Inactivation at High Temperatures and Regeneration of Green Asparagus Peroxidase

1996 ◽  
Vol 59 (10) ◽  
pp. 1065-1071 ◽  
Author(s):  
CARMEN RODRIGO ◽  
MIGUEL RODRIGO ◽  
ANDRÉS ALVARRUIZ ◽  
ANA FRÍGOLA
Keyword(s):  
Enzyme Activity ◽  
Peroxidase Activity ◽  
Thermal Inactivation ◽  
Maximum Activity ◽  
Small Samples ◽  
Inactivation Kinetics ◽  
Optimum Conditions ◽  
First Order ◽  
Kinetics Of ◽  
Green Asparagus

A spectrophotometric method was developed for determining the peroxidase activity of green asparagus in small samples. The optimum conditions for the analysis in the cuvette were 45 mM of H2O2 36 mM of guaiacol, and pH 7. The method can be used to determine enzyme activity at up to two decimal reductions. A study was performed of the regeneration and inactivation kinetics of the enzyme when heated between 90 and 125°C. Regenerated asparagus peroxidase reached its maximum activity after being stored 6 days at 25°C. The regenerated enzyme followed first-order inactivation kinetics, showing an Ea = 13.62 kcal/mol and k100°C = 2.07 min−1.

Properties of inward calcium current in guinea pig ureteral myocytes

1997 ◽  
Vol 272 (2) ◽  
pp. C543-C549 ◽  
Author(s):  
J. L. Sui ◽  
C. Y. Kao
Keyword(s):  
Action Potentials ◽  
Calcium Current ◽  
Inactivation Kinetics ◽  
Slow Inactivation ◽  
Time Constants ◽  
Channel Inactivation ◽  
Steady State Inactivation ◽  
Window Current ◽  
Kinetics Of ◽  
Ca2 Channels

Ureteral myocytes of guinea pigs have L-type Ca2+ channels (I(Ca)). In 3 mM Ca2+, maximum I(Ca) was 3.38 microA/cm2. Voltage at which conductance is 50% of maximum (V0.5) of I(Ca) was -1.0 mV in 3 mM Ca2+ and +22 mV in 30 mM Ca2+, with slope factors of 8 mV. V0.5 of steady-state inactivation of I(Ca) was -16.2 and +1.1 mV in 3 and 30 mM Ca2+, respectively, with similar slope factors of about -6 mV. A window current reaching 20-25% of the maximum I(Ca) was active between -20 and 0 mV. I(Ca) inactivated very slowly, with time constants of 217.6 and 2,455.9 ms with no voltage dependency. When Ba2+ was used as the charge carrier, the amplitude and inactivation kinetics of the Ba2+ current were similar to those for I(Ca). These results indicate that the ureteral myocyte has little Ca2+-mediated Ca2+ channel inactivation, a feature significantly associated with the slow I(Ca) inactivation. The slow inactivation and the window current are essential for the sustained membrane depolarization during the plateau of ureteral action potentials.

scholarly journals Fast and Slow Inactivation Kinetics of the Ca2+Channels ECaC1 and ECaC2 (TRPV5 and TRPV6)

2002 ◽  
Vol 277 (34) ◽  
pp. 30852-30858 ◽  
Author(s):  
Bernd Nilius ◽  
Jean Prenen ◽  
Joost G. J. Hoenderop ◽  
Rudi Vennekens ◽  
Susan Hoefs ◽  
...  
Keyword(s):  
Inactivation Kinetics ◽  
Slow Inactivation ◽  
Kinetics Of ◽  
Ca2 Channels

scholarly journals Inactivation kinetics of dihydrofolate reductase from Chinese hamster during urea denaturation

1997 ◽  
Vol 324 (2) ◽  
pp. 395-401 ◽  
Author(s):  
Jia-Wei WU ◽  
Zhi-Xin WANG ◽  
Jun-Mei ZHOU
Keyword(s):  
Enzyme Activity ◽  
Dihydrofolate Reductase ◽  
Single Phase ◽  
Tertiary Structure ◽  
Chinese Hamster ◽  
Free Enzyme ◽  
Inactivation Kinetics ◽  
Binary And Ternary Complexes ◽  
Enzyme Substrate ◽  
Kinetics Of

The kinetic theory of substrate reaction during modification of enzyme activity has been applied to the study of inactivation kinetics of Chinese hamster dihydrofolate reductase by urea [Tsou (1988) Adv. Enzymol. Relat. Areas Mol. Biol. 61, 381–436]. On the basis of the kinetic equation of substrate reaction in the presence of urea, all microscopic kinetic constants for the free enzyme and enzyme–substrate binary and ternary complexes have been determined. The results of the present study indicate that the denaturation of dihydrofolate reductase by urea follows single-phase kinetics, and changes in enzyme activity and tertiary structure proceed simultaneously in the unfolding process. Both substrates, NADPH and 7,8-dihydrofolate, protect dihydrofolate reductase against inactivation, and enzyme–substrate complexes lose their activity less rapidly than the free enzyme.

scholarly journals Formation of an unstable covalent intermediate during the inhibition of electric-eel acetylcholinesterase with 1,3,2-dioxaphosphorinane 2-oxides

1979 ◽  
Vol 177 (3) ◽  
pp. 781-790 ◽  
Author(s):  
Y Ashani ◽  
H Leader
Keyword(s):  
Active Site ◽  
Cyclic Acid ◽  
Leaving Group ◽  
Electric Eel ◽  
Activation Profile ◽  
Covalent Intermediate ◽  
Kinetics Of ◽  
Fluoro Derivatives ◽  
Enzyme Intermediate ◽  
Inhibited Enzyme

The kinetics of interaction of eel acetylcholinesterase (EC 3.1.1.7) with 1,3,2-dioxaphosphorinane 2-oxides were investigated. It was demonstrated that the rate of spontaneous re-activation as well as the re-activation profile in the presence of 2-pyridine aldoxime methiodide of the inhibited enzyme are irrespective of the leaving group of three inhibitors and exhibit the same values. The dissociation constant of the corresponding Michaelis complex was evaluated by two independent methods and the results were found to be in close agreement. It was shown that the active site is essential for interaction between the enzyme and the various dioxaphosphorinanes. The mixed anhydride of diethyl phosphoric acid and 2-hydroxy-1,3,2-dioxaphosphorinane 2-oxide behaves exactly as would be predicted from a typical diethyl phosphate inhibitor. Enxyme that was incubated with the cyclic acid or the corresponding methyl ester recovered immediately upon extensive dilution. Inhibition of enzyme in the presence of high concentratasions of the corresponding 2-chloro and 2-fluoro derivatives decreased the regeneration rates as well as the maximal amount of the re-activated enzyme. This observation could not be explained in terms of a classical aging process. On the basis of the kinetics observations it is suggested that an unstable covalent phospho-enzyme intermediate is formed during the reaction between acetylcholinesterase and 1,3,2-dioxaphosphorinane 2-oxides.

scholarly journals Development of MTH1-Binding Nucleotide Analogs Based on 7,8-Dihalogenated 7-Deaza-dG Derivatives

2021 ◽  
Vol 22 (3) ◽  
pp. 1274
Author(s):  
Hui Shi ◽  
Ren Ishikawa ◽  
Choon Han Heh ◽  
Shigeki Sasaki ◽  
Yosuke Taniguchi
Keyword(s):  
Enzyme Activity ◽  
Active Site ◽  
Inhibitory Effects ◽  
Nucleotide Analogs ◽  
Computational Docking ◽  
Drug Candidates ◽  
Repair Enzymes ◽  
Nucleotide Pools ◽  
New Compounds ◽  
Inhibited Enzyme

MTH1 is an enzyme that hydrolyzes 8-oxo-dGTP, which is an oxidatively damaged nucleobase, into 8-oxo-dGMP in nucleotide pools to prevent its mis-incorporation into genomic DNA. Selective and potent MTH1-binding molecules have potential as biological tools and drug candidates. We recently developed 8-halogenated 7-deaza-dGTP as an 8-oxo-dGTP mimic and found that it was not hydrolyzed, but inhibited enzyme activity. To further increase MTH1 binding, we herein designed and synthesized 7,8-dihalogenated 7-deaza-dG derivatives. We successfully synthesized multiple derivatives, including substituted nucleosides and nucleotides, using 7-deaza-dG as a starting material. Evaluations of the inhibition of MTH1 activity revealed the strong inhibitory effects on enzyme activity of the 7,8-dihalogenated 7-deaza-dG derivatives, particularly 7,8-dibromo 7-daza-dGTP. Based on the results obtained on kinetic parameters and from computational docking simulating studies, these nucleotide analogs interacted with the active site of MTH1 and competitively inhibited the substrate 8-oxodGTP. Therefore, novel properties of repair enzymes in cells may be elucidated using new compounds.

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