Substrate (chemistry)

About: Substrate (chemistry) is a research topic. Over the lifetime, 35902 publications have been published within this topic receiving 740722 citations. The topic is also known as: enzyme substrate.

Inhibition of catechol 2,3-dioxygenase from Pseudomonas putida by 3-chlorocatechol.

Abstract: Partially purified preparations of catechol 2,3-dioxygenase from toluene-grown cells of Pseudomonas putida catalyzed the stoichiometric oxidation of 3-methylcatechol to 2-hydroxy-6-oxohepta-2,4-dienoate. Other substrates oxidized by the enzyme preparation were catechol, 4-methylcatechol, and 4-fluorocatechol. The apparent Michaelis constants for 3-methylcatechol and catechol were 10.6 and 22.0 muM, respectively. Substitution at the 4-position decreases the affinity and activity of the enzyme for the substrate. Catechol 2,3-dioxygenase preparations did not oxidize 3-chlorocatechol. In addition, incubation of the enzyme with 3-chlorocatechol led to inactivation of the enzyme. Kinetic analyses revealed that both 3-chlorocatechol and 4-chlorocatechol were noncompetitive or mixed-type inhibitors of the enzyme. 3-Chlorocatechol (Ki = 0.14 muM) was a more potent inhibitor than 4-chlorocatechol (Ki = 50 muM). The effect of the ion-chelating agents Tiron and o-phenanthrolene were compared with that of 3-chlorocatechol on the inactivation of the enzyme. Each inhibitor appeared to remove iron from the enzyme, since inactive enzyme preparations could be fully reactivated by treatment with ferrous iron and a reducing agent.

Classification of beta-lactamases: groups 1, 2a, 2b, and 2b'.

Abstract: Information on 3-lactamases has grown rapidly within the past few years, such that it has become difficult to make meaningful comparisons between well-established P-lactamases and those enzymes recently identified. The intention of this review, therefore, is to present a compilation of data that will be useful in establishing a set of unique characteristics for many of the f3-lactamases that have been described in the primary literature (also see reference 14). The criteria used for characterization are discussed elsewhere (13).

Substrate inhibition of acetylcholinesterase: residues affecting signal transduction from the surface to the catalytic center.

Abstract: Amino acids located within and around the 'active site gorge' of human acetylcholinesterase (AChE) were substituted. Replacement of W86 yielded inactive enzyme molecules, consistent with its proposed involvement in binding of the choline moiety in the active center. A decrease in affinity to propidium and a concomitant loss of substrate inhibition was observed in D74G, D74N, D74K and W286A mutants, supporting the idea that the site for substrate inhibition and the peripheral anionic site overlap. Mutations of amino acids neighboring the active center (E202, Y337 and F338) resulted in a decrease in the catalytic and the apparent bimolecular rate constants. A decrease in affinity to edrophonium was observed in D74, E202, Y337 and to a lesser extent in F338 and Y341 mutants. E202, Y337 and Y341 mutants were not inhibited efficiently by high substrate concentrations. We propose that binding of acetylcholine, on the surface of AChE, may trigger sequence of conformational changes extending from the peripheral anionic site through W286 to D74, at the entrance of the 'gorge', and down to the catalytic center (through Y341 to F338 and Y337). These changes, especially in Y337, could block the entrance/exit of the catalytic center and reduce the catalytic efficiency of AChE.

Structure and mechanism of para-hydroxybenzoate hydroxylase.

Abstract: Para-hydroxybenzoate hydroxylase (EC 114132) is a flavoprotein involved in degradation of aromatic compounds, and it has become a model for enzymes involved in the oxygenation of a substrate The chemical and kinetic mechanisms of this enzyme are described and integrated with an outline of the structure of the protein from crystallographic analysis The structure is unusual because there is no recognizable domain for the binding of NADPH involved in the reaction Recently, mechanistic studies of site-directed mutants, combined with structural analyses, have provided some exciting discoveries about protein function The substrate during catalysis is largely isolated from solvent in the active site, a necessary condition for successful product formation The flavin ring structure moves substantially in the active site, probably to enable substrate and product exchange into this site and possibly to regulate the reduction of the flavin by NADPH A chain of H-bonds can connect p-hydroxy-benzoate in the act