Re-evaluation of the Inhibition Constants of Previously Investigated Competitive Inhibitors of α-Chymotrypsin. I. Hydrolysis Products and Enantiomorphs of Previously Investigated Specific Substrates1

1955 ◽  
Vol 77 (9) ◽  
pp. 2378-2383 ◽  
Author(s):  
Robert J. Foster ◽  
Henry J. Shine ◽  
Carl Niemann
Keyword(s):  
Hydrolysis Products ◽  
Competitive Inhibitors ◽  
Inhibition Constants

Di- and tripeptide N-alkyl- and N-aralkyl amides as chymotrypsin inhibitors

1988 ◽  
Vol 53 (11) ◽  
pp. 2877-2883 ◽  
Author(s):  
Evžen Kasafírek ◽  
Irena Šutiaková ◽  
Michal Bartík ◽  
Antonín Šturc
Keyword(s):  
Methyl Ethyl ◽  
Competitive Inhibitors ◽  
Inhibition Constants ◽  
Chymotrypsin Inhibitors

Two competitive inhibitors of chymotrypsin, Glt-Ala-Ala-Leu-EtPh and Glt-Ala-Ala-Pro-NH-EtPh, were synthesized and their inhibition constants Ki were determined. The Ki-determination was carried also with a set of peptides of type X-(Ala)nNH-Y, where X is 3-carboxypropionyl- or 4-carboxybutyryl-, n is 2 or 3 and Y is methyl, ethyl, diethyl, isopropyl, propyl, butyl, isobutyl and 2-phenylethyl. Chymotrypsin inhibition was observed only with peptides containing an aralkyl residue whereas peptides with an alkyl are without any effect. Glt-Ala-Ala-Leu-NH-EtPh shows the highest Ki-value (80 μmol l-1).

scholarly journals Interaction of the lacZ β-galactosidase of Escherichia coli with some β-d-galactopyranoside competitive inhibitors

1979 ◽  
Vol 177 (1) ◽  
pp. 145-152 ◽  
Author(s):  
R. S. Thomas Loeffler ◽  
Michael L. Sinnott ◽  
Brian D. Sykes ◽  
Stephen G. Withers
Keyword(s):  
Escherichia Coli ◽  
Competitive Inhibition ◽  
Phenolic Hydroxy Group ◽  
Bivalent Metal ◽  
Transverse Relaxation ◽  
Competitive Inhibitors ◽  
Inhibition Constants ◽  
Increasing Temperature ◽  
Phenolic Hydroxy ◽  
Average Position

1. The location of the bivalent metal cation with respect to bound competitive inhibitors in Escherichia coli (!lacZ) β-galactosidase was investigated by proton magnetic resonance. 2. Replacement of Mg2+ by Mn2+ enhances both longitudinal and transverse relaxation of the methyl groups of the β-d-galactopyranosyltrimethylammonium ion, and of methyl 1-thio-β-d-galactopyranoside; linewidths are narrowed by increasing temperature. 3. The Mn2+ ion is located 8–9Å (0.8–0.9nm) from the centroid of the trimethylammonium group and 9Å (0.9nm) from the average position of the methylthio protons. 4. The effective charge at the active site was probed by measurement of competitive inhibition constants (Kio and Ki+ respectively) for the isosteric ligands, β-d-galactopyranosylbenzene and the β-d-galactopyranosylpyridinium ion. 5. The ratio of inhibition constants (Q=Ki+/Kio) obtained with 2-(β-d-galactopyranosyl)–naphthalene and the β-d-galactopyranosylisoquinolinium ion at pH7 with Mg2+–enzyme was identical, within experimental error, with that obtained with the monocyclic compounds. 6. The variation of Q for Mg2+–enzyme can be described by Q=0.1(1+[H+]/4.17×10−10)/1+[H+]/10−8). 7. This, in the theoretical form for a single ionizable group, is ascribed to the ionization of the phenolic hydroxy group of tyrosine-501. 8. The variation of Q for Mg2+-free enzyme is complex, probably because of deprotonation of the groups normally attached to Mg2+ as well as tyrosine-501.

scholarly journals 7-Deazapurine 2'-deoxyribofuranosides are noncleavable competitive inhibitors of Escherichia coli purine nucleoside phosphorylase (PNP).

1998 ◽  
Vol 45 (3) ◽  
pp. 755-768 ◽  
Author(s):  
A Bzowska ◽  
Z Kazimierczuk ◽  
F Seela
Keyword(s):  
Escherichia Coli ◽  
Purine Nucleoside Phosphorylase ◽  
Modified Nucleosides ◽  
Purine Nucleoside ◽  
Preliminary Screening ◽  
Nucleoside Phosphorylase ◽  
E Coli ◽  
Potent Inhibition ◽  
Competitive Inhibitors ◽  
Inhibition Constants

A series of 7-deazapurine 2'-deoxyribofuranosides were synthesized according to already known procedures and their substrate and inhibitor properties with purified E. coli purine nucleoside phosphorylase were examined. In agreement with previous findings, substrate activity was not detected for any of the compounds tested. Most of the nucleosides showed weak inhibition in the preliminary screening, i.e. at a concentration of about 100 microM. However some combinations of 6-chloro, 6-amino or 6-methoxy substituents with bulky hydrophobic groups at position 7 of the base and/or chloro, amino, methoxy or methylthio group at position 2 markedly enhanced affinity of such modified nucleosides for the E. coli enzyme. The most potent inhibition was observed for two nucleosides: 6-chloro- and 2-amino-6-chloro-7-deazapurine 2'-deoxyribofuranosides that show inhibition constants Ki = 2.4 and 2.3 microM, respectively. Several other compounds were also found to be good inhibitors, with inhibition constants in the range 5-50 microM. In all instances the inhibition was competitive vs. the nucleoside substrate 7-methylguanosine. Inhibition constants for 7-deazapurine nucleosides are in general several-fold lower than those observed for their purine counterparts. Therefore 7-deaza modification together with substitutions at positions 2, 6 and 7 of the base is a very promising approach to obtain competitive noncleavable inhibitors of E. coli PNP that may bind to the enzyme with inhibition constants in the microM range.

A human cytochrome P-450 characterized by inhibition studies as the sparteine–debrisoquine monooxygenase

1984 ◽  
Vol 62 (7) ◽  
pp. 860-862 ◽  
Author(s):  
T. Inaba ◽  
M. Nakano ◽  
S. V. Otton ◽  
W. A. Mahon ◽  
W. Kalow
Keyword(s):  
Correlation Coefficient ◽  
Human Liver ◽  
Liver Microsomes ◽  
Human Liver Microsomes ◽  
Human Cytochrome ◽  
Competitive Inhibitors ◽  
Inhibition Constants ◽  
Inhibition Studies ◽  
Cytochrome P 450

The present study compares the debrisoquine monooxygenase and the sparteine monooxygenase activities of human liver microsomes. In the presence of 14 competitive inhibitors, apparent inhibition constants (Ki) as determined by these two activities ranged over four orders of magnitude with a correlation coefficient 0.99. These in vitro results represent the strongest evidence to date that the debrisoquine monooxygenase and the sparteine monooxygenase are identical and involve a single isozyme of cytochrome P-450.

scholarly journals Characterization of Maltase and Sucrase Inhibitory Constituents from Rhodiola crenulata

Foods ◽  
2019 ◽  
Vol 8 (11) ◽  
pp. 540 ◽  
Author(s):  
Wen-Tai Li ◽  
Yu-Hsuan Chuang ◽  
Jung-Feng Hsieh
Keyword(s):  
Inhibitory Activity ◽  
Inhibitory Concentration ◽  
Epicatechin Gallate ◽  
Competitive Inhibitors ◽  
Inhibition Kinetic ◽  
Ic50 Values ◽  
Rhodiola Crenulata ◽  
Inhibition Constants

The inhibitory properties of epicatechin-(4β,8)-epicatechingallate (B2-3’-O-gallate), epicatechin gallate (ECG), and epicatechin (EC) isolated from Rhodiola crenulata toward maltase and sucrase were investigated. The half-maximal inhibitory concentration (IC50) values for maltase were as follows: B2-3’-O-gallate (1.73 ± 1.37 μM), ECG (3.64 ± 2.99 μM), and EC (6.25 ± 1.84 μM). Inhibition kinetic assays revealed the inhibition constants (Ki) of the mixed-competitive inhibitors of maltase, as follows: B2-3’-O-gallate (1.99 ± 0.02 μM), ECG (3.14 ± 0.04 μM), and EC (7.02 ± 0.26 μM). These compounds also showed a strong inhibitory activity toward sucrase, and the IC50 values of B2-3’-O-gallate, ECG, and EC were 6.91 ± 3.41, 18.27 ± 3.99, and 18.91 ± 3.66 μM, respectively. Inhibition kinetic assays revealed the inhibition constants (Ki) of the mixed-competitive inhibitors of sucrase as follows: B2-3’-O-gallate (6.05 ± 0.04 μM), ECG (8.58 ± 0.08 μM), and EC (13.72 ± 0.15 μM). Overall, these results suggest that B2-3’-O-gallate, ECG, and EC are potent maltase and sucrase inhibitors.

scholarly journals A simple graphical method for determining the inhibition constants of mixed, uncompetitive and non-competitive inhibitors (Short Communication)

1974 ◽  
Vol 137 (1) ◽  
pp. 143-144 ◽  
Author(s):  
Athel Cornish-Bowden
Keyword(s):  
Short Communication ◽  
Graphical Method ◽  
Competitive Inhibitor ◽  
Inhibition Constant ◽  
New Method ◽  
Competitive Inhibitors ◽  
Inhibition Constants ◽  
Inhibited Enzyme

A new method is described for plotting kinetic results for inhibited enzyme-catalysed reactions. It provides a simple way of determining the inhibition constant, K′i, of an uncompetitive, mixed or non-competitive inhibitor.

Kinetic Study of the Effect of Heparin on the Amidase Activity of Trypsin, Plasmin and Urokinase

1983 ◽  
Vol 49 (03) ◽  
pp. 199-203 ◽  
Author(s):  
V M Yomtova ◽  
N A Stambolieva ◽  
B M Blagoev
Keyword(s):  
Kinetic Study ◽  
Active Center ◽  
Simultaneous Presence ◽  
Amidase Activity ◽  
Competitive Inhibitors ◽  
Uncompetitive Inhibitor

SummaryIt was found that the effect of heparin on the amidase activity of urokinase (E C 3.4.21.31), plasmin (E C 3.4.21.7) and trypsin (E C 3.4.21.4) depended on the substrate used. No effect of heparin on the amidase activity of urokinase and trypsin was observed when Pyro Glu-Gly-Arg-p-nitroanilide (S-2444) and α-N-acetyl-L-lysine-p-nitroanilide (ALNA) were used as substrates. Heparin acted as a uncompetitive inhibitor of trypsin (Ki = 1.2×10-6 M), plasmin (Ki = 4.9×10-6 M) and urokinase (Ki = l.0×10-7 M) when Bz-Phe-Val-Arg-p-nitroanilide (S-2160), H-D-Val-Leu-Lys-p-nitroanilide (S-2251) and plasminogen, respectively, were used as substrates. These results, as well as the data obtained by studying the effect of the simultaneous presence of heparin and competitive inhibitors suggest that although heparin is not bound at the active center of these enzymes, it may influence the effectivity of catalysis.

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