Enzyme Catalysis
Mostrando 37-48 de 558 artigos, teses e dissertações.
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37. Structural and Biochemical Evidence That a TEM-1 β-Lactamase N170G Active Site Mutant Acts via Substrate-assisted Catalysis*
TEM-1 β-lactamase is the most common plasmid-encoded β-lactamase in Gram-negative bacteria and is a model class A enzyme. The active site of class A β-lactamases share several conserved residues including Ser70, Glu166, and Asn170 that coordinate a hydrolytic water involved in deacylation. Unlike Ser70 and Glu166, the functional significance of residue As
American Society for Biochemistry and Molecular Biology.
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38. Directional Character of Proton Transfer in Enzyme Catalysis*
Hydrogen bonding can facilitate proton transfer in certain directions and retard proton transfer in certain other directions. By assuming that directed proton transfer along strategically oriented hydrogen bonds in the enzyme-substrate complex plays an important role in determining the efficiency and specificity of the enzyme, we present a unified interpreta
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39. Dual role of interfacial phospholipid in phospholipase A2 catalysis.
The results of crosslinking experiments with dimethyl suberimidate and gel filtration binding studies are used to delineate a detailed model for phospholipase A2(phosphatide 2-acyl-hydrolase, EC 3.1.1.4) action in the presence of Ca2+ on mixed micelles of Triton X-100 and phospholipid. Important features of the "dual-phospholipid" model are: (i) the use of t
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40. Carbon Dioxide Hydration Activity of Carbonic Anhydrase: Paradoxical Consequences of the Unusually Rapid Catalysis*
The kinetic parameters for carbon dioxide hydration catalysis by carbonic anhydrase (EC 4.2.1.1) present an apparent paradox. The assumption of H2CO3 as the hydration product requires the rate of recombination of H2CO3 with enzyme to be faster than the diffusion limit. The alternative assumption of HCO3- as the product of hydration likewise requires active-s
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41. On the active site thiol of gamma-glutamylcysteine synthetase: relationships to catalysis, inhibition, and regulation.
gamma-Glutamylcysteine synthetase (glutamate-cysteine ligase; EC 6.3.2.2) was isolated from an Escherichia coli strain enriched in the gene for this enzyme by recombinant DNA techniques. The purified enzyme has a specific activity of 1860 units/mg and a molecular weight of 56,000. Comparison of the E. coli enzyme with the well-characterized rat kidney enzyme
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42. An enzymatic molten globule: Efficient coupling of folding and catalysis
A highly active, monomeric chorismate mutase, obtained by topological redesign of a dimeric helical bundle enzyme from Methanococcus jannaschii, was investigated by NMR and various other biochemical techniques, including H/D exchange. Although structural disorder is generally considered to be incompatible with efficient catalysis, the monomer, unlike its nat
National Academy of Sciences.
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43. Dynamics of enzymatic reactions.
The detailed molecular dynamics of an actual bond-breaking event in a fluctuating enzyme substrate complex is simulated. The method developed allows one to explore what type of fluctuations are involved in enzymatic reactions and to evaluate entropic contributions to enzyme catalysis. The fluctuations of the enzyme electrostatic potential are found to be a k
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44. Directed evolution of an extremely fast phosphotriesterase by in vitro compartmentalization
We describe the selection of a phosphotriesterase with a very fast kcat (over 105 s–1), 63 times higher than the already very efficient wild-type enzyme. The enzyme was selected from a library of 3.4 × 107 mutated phosphotriesterase genes using a novel strategy based on linking genotype and phenotype by in vitro compartmentalization (IVC) using water-in-
Oxford University Press.
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45. Structure and mechanism of action of a novel phosphoglycerate mutase from Bacillus stearothermophilus
Bacillus stearothermophilus phosphoglycerate mutase (PGM), which interconverts 2- and 3–phosphoglyceric acid (PGA), does not require 2,3–diphosphoglyceric acid for activity. However, this enzyme does have an absolute and specific requirement for Mn2+ ions for catalysis. Here we report the crystal structure of this enzyme complexed with 3PGA and manganese
Oxford University Press.
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46. Vitamin K2 (menaquinone) biosynthesis in Escherichia coli: evidence for the presence of an essential histidine residue in o-succinylbenzoyl coenzyme A synthetase.
o-Succinylbenzoyl coenzyme A (OSB-CoA) synthetase, when treated with diethylpyrocarbonate (DEP), showed a time-dependent loss of enzyme activity. The inactivation follows pseudo-first-order kinetics with a second-order rate constant of 9.2 x 10(-4) +/- 1.4 x 10(-4) microM(-1) min(-1). The difference spectrum of the modified enzyme versus the native enzyme sh
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47. Use of intrinsic binding energy for catalysis by an RNA enzyme
The contribution of several individual ribozyme⋅substrate base pairs to binding and catalysis has been investigated using hammerhead ribozyme substrates that were truncated at their 3′ or 5′ ends. The base pairs at positions 1.1–2.1 and 15.2–16.2, which flank the conserved core, each contribute 104-fold in the chemical step, without affecting subst
The National Academy of Sciences of the USA.
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48. Evolution of an enzyme active site: The structure of a new crystal form of muconate lactonizing enzyme compared with mandelate racemase and enolase
Muconate lactonizing enzyme (MLE), a component of the β-ketoadipate pathway of Pseudomonas putida, is a member of a family of related enzymes (the “enolase superfamily”) that catalyze the abstraction of the α-proton of a carboxylic acid in the context of different overall reactions. New untwinned crystal forms of MLE were obtained, one of which diffrac
The National Academy of Sciences.