Search results for "competitive inhibition"
showing 8 items of 28 documents
Thymidylate synthases from Hymenolepis diminuta and regenerating rat liver: purification, properties, and inhibition by substrate and cofactor analog…
1995
Comparative studies of thymidylate synthases, isolated from the tapeworm, Hymenolepis diminuta, and regenerating liver of its host, rat, aimed at a possibility of specific inhibition of the helminthic enzyme, are presented. While similar in structure (dimers with monomer molecular masses of 33.7 kDa and 34.9 kDa, respectively) and parameters describing interactions with substrates and products, the tapeworm and rat enzymes differed in the dependences of reaction velocity on temperature (Arrhenius plots biphasic and linear, respectively). The tapeworm, compared with the host, enzyme was less sensitive to the competitive slow-binding inhibition by 5-fluoro-dUMP and its 2-thio congener, but eq…
l-Tyrosine β-naphthylamide is a potent competitive inhibitor of tyramine N-(hydroxycinnamoyl)transferase in vitro
2001
L-Tyrosine beta-naphthylamide, a synthetic substrate designed to measure tyrosine aminopeptidase activity, is a potent inhibitor of hydroxycinnamoyl-CoA:tyramine N-(hydroxycinnamoyl)transferase (THT) purified from elicited tobacco cell-suspension cultures. The inhibition is competitive, with the inhibitor binding reversibly to the tyramine binding site of the enzyme. Similar results were obtained with THT extracted from elicited potato cell-suspension cultures. Ki values were found to be 0.66 microM for the enzyme from tobacco and 0.3 microM for the enzyme from potato. L-Tyrosine 7-amido-4-methylcoumarin, a fluorogenic substrate for tyrosine aminopeptidases, the structure of which is close …
Monoamine Oxidase Inhibition by β-Carbolines: A Quantum Chemical Approach
1979
Monoamine oxidase inhibition by beta-carboline derivatives is related to the energy change, delta E, arising from complex formation between the inhibitor and the enzyme. The energy change was expressed in terms of electronic indexes, which were estimated for a set of aromatic beta-carbolines. The electronic indexes were correlated to the experimental activity indexes by a simplified quantum chemical perturbational treatment with a multiple regression procedure. A characteristic structure for the inhibitor-enzyme complex was derived from the correlation. The molecules are linked by two kinds of bond. One involves the lone pyridine nitrogen pair of beta-carbolines; the other is due to a pi-el…
Kinetic properties of hexameric tyrosinase from the crustacean Palinurus elephas.
2008
Tyrosinases catalyze hydroxylation of monophenols to o-diphenols and their subsequent oxidation to o-quinones, whereas catecholoxidases catalyze only the latter reaction. Both enzymes occur in all organisms and are Type 3 copper proteins that perform the first steps of melanin formation. In arthropods, they play an essential role in the sclerotization of the exoskeleton. Very few phenoloxidases are characterized structurally or kinetically and the existence of an actual tyrosinase activity has not been demonstrated in most cases. Here we present for the first time a complete kinetic characterization of a tyrosinase from a crustacean (Palinurus elephas) including the influence of inhibitors.…
Trichinella spiralisThymidylate Synthase: Developmental Pattern, Isolation, Molecular Properties, and Inhibition by Substrate and Cofactor Analogues
1996
Abstract Thymidylate synthase specific activity was found to remain at a constant level in crude extracts from muscle larvae, isolated (1-15 months after infection) by pepsin-HCl digestion, as well as from adult worms ofTrichinella spiralis.The enzyme was purified and its molecular (monomer mol. wt 35 kD) and kinetic (sequential mechanism with the Kmvalues 3.1 and 19 μM for dUMP and N5,10-methylenetetrahydrofolate, respectively) properties determined. 5-Fluoro-dUMP was a competitive, slow-binding inhibitor of the parasite enzyme. N5,10-methylenetetrahydrofolate analogues 10-propargyl-5,8-dideazafolate (CB3717), ZD1694, BW1843U89, and AG337 were weaker inhibitors of the parasite than regener…
Control of the thermal reaction of a photochromic spirobenzopyran by the enzyme-like activity of albumins
1997
Abstract The thermal ring-opening reaction of a negative photochronic spirobenzopyran was investigated in the presence and absence of albumins. In the presence of the proteins, the formation of the merocyanine form from the spiro form is enhanced markedly by two orders of magnitude. The results for five different albumins indicate the enzyme-like activity of the proteins. The influence of pH, temperature and various ligands was examined in detail for bovine serum albumin (BSA) and human serum albumin (HSA). In particular, it was deduced that warfarin shows reversible purely competitive inhibition for BSA with an inhibitor constant K 1 of 1.6×10 −3 M. The results suggest that the catalytic c…
DRUG-DRUG INTERACTIONS VIA INHIBITION OF MICROSOMAL ENZYMES INVOLVED IN METABOLISM OF EPOXIDES PRODUCED BY MICROSOMAL MONOOXYGENASE
1977
SUMMARY Benzo(a)pyrene was activated by liver microsomes to mutagens detected by the reversion of histidine dependent Salmonella typhimurium TA 1537. Using pure epoxide hydratase or epoxide hydratase inhibitors, comparing animal species with high and low epoxide hydratase activity, or inducing monooxygenase activity, it was shown that epoxide hydratase was a critical enzyme for the inactivation of these mutagens. Many clinically used drugs are metabolized to epoxides. Epoxides are not necessarily mutagenic, but since epoxide hydratase has a very low substrate specificity, such epoxides may competitively inhibit the hydration of mutagenic epoxides, as demonstrated in the present study for th…
Modelling of the cometabolic decomposition of 4-chlorophenol and phenol by the Stenotrophomonas maltophilia KB2 strain
2017
Zaprezentowano model rozkładu 4-chlorofenolu przez szczep Stenotrophomonas maltophilia KB2 w obecności fenolu jako substratu wzrostowego. Opracowanie tego modelu wymagało wykonania czterech serii badań: biodegradacji różnych dawek czystego fenolu, biodegradacji różnych dawek czystego 4-CP, biodegradacji 4-CP w obecności fenolu przy różnym stosunku stężeń obu substratów oraz biodegradacji 4-CP przez komórkiw fazie spoczynku, indukowane wstępnie fenolem. Szczegółowo omówiono sposoby wyznaczania poszczególnych parametrów równań opisujących szybkość degradacji substratów wzrostowego i niewzrostowego oraz przyrostu biomasy. W oparciu o stworzoną bazę danych obliczono m.in. stałe półnasycenia KSg…