Strain and distortion

The binding of the substrate results in a distortion of the substrate (pulling or pushing on a bond) in a way that makes the chemical reaction easier. 

In this model, the binding of the substrate to the enzyme strains specific chemical bonds, making the subsequent chemical reaction easier. If a bond has to be broken, the enzyme grabs onto both sides of the bond and pulls. If a bond has to be formed, the enzyme grabs onto both sides and pushes. By this model, the enzyme must be designed to apply the strain in the right direction— the direction that will help convert the reactant to the transition state (Fig. 7-5). 

Strynadka, N. C. J., and James, M. N. G. Lysozyme Revisited Crystallographic Evidence for Distortion of an N-Acetylmuramic Acid Residue Bound in Site D. /. Mol. Biol., 220,401-424 (1991). Kuroko, R., Weaver, 

and Matthews, B. W. A Covalent Enzyme-Substrate Intermediate with Saccharide Distortion in a Mutant T4 Lysozyme. Science, 262,2030-2033(1993). 

Now one lone pair is synperiplanar with the leaving group OH 

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Finally, in the sense that the imposition of conformational restrictions or specific solvent effects on an organic molecule are forms of strain, non-covalent catalysis by the cycloamyloses may provide a simple model for the investigation of strain and distortion effects in enzymatic reactions. 

One type of point defect that cannot be entirely eliminated from a solid compound is the substituted ion or impurity defect. For example, suppose a large crystal contains 1 mole of NaCl that is 99.99 mole percent pure and that the 0.01% impurity is KBr. As a fraction, there is 0.0001 mole of both K+ and Br ions, which is 6.02 X 1019 ions of each type present in the 1 mole of NaCl Although the level of purity of the NaCl is high, there is an enormous number of impurity ions that occupy sites in the lattice. Even if the NaCl were 99.9999 mole percent pure, there would still be 6.02 X 1017 impurity cations and anions in a mole of crystal. In other words, there is a defect, known as a substituted ion or impurity defect, at each point in the crystal where some ion other than Na+ or Cl- resides. Because K+ is larger than Na+ and Br is larger than Cl-, the lattice will experience some strain and distortion at the sites where the larger cations and anions reside. These strain points are frequently reactive sites in a crystal. 

Strain and Distortion Transition-State Stabilization Transition-State Analogs Chemical Catalysis... 

The STRAIN AND DISTORTION model for catalysis involves pushing, pulling, or twisting a bond that is to be made or broken during the reaction. Parts of the substrate not involved directly in the chemical reaction are required to hold the substrate on the enzyme in the distorted form. The distortion and strain make it easier to reach the transition state. 

Using the bulk and shear modulus to relate dilational stress to dilational strain and distortional stress to distortional strain yields ... 

Strain and distortion The substrate molecule, by forming the enzyme-substrate complex, is forced toward the geometry of the transition state since the enzyme may bind the transition-state-like structure favorably (Secemski and Lienhard,... 

Strain and distortion An enzyme is able to accelerate a chemical reaction by having evolved an active site that is exquisitely complementary to the transition state. Although an active site must bind subsdate, it is in the transition state that the binding interactions with the enzyme are maximized. To this objective, the substrate molecule is distorted to that of the transition state structure (Strynadka and James, 1991). 

Strain and distortion have also been utilized to achieve large rate accelerations with antibodies. In this strategy, antibody binding energy is used to force a substrate into a destabilizing microenvironment. For example, antibodies are raised against an A-methylated... 

Jencks argued that almost certainly strain and distortion produced in the reactants by the enzymes contribute to the catalysis brought about by these enzymes (Jencks, 1969). For an informative development of this thesis the reader is referred to the original work by Jencks. The idea is inherently plausible, but, as noted (Jencks, 1969), is difficult to test experimentally. No such evaluation has yet been provided in a case of a transmethylation reaction and the role of the enzyme proteins in enhancement of methyl transfers remains almost totally obscure. 

The authors used several octahedral distortion parameters [83], such as shear strain and distortion index, to describe ZrOg octahedra and assign the two Zr SSNMR resonances to crystallographic sites within... 

These structural features, however, are limited to idealized geometric arrangements. Real stmctures of clay minerals contain substantial crystal strains and distortions, which lead to irregularities such as deformed octahedra and tetrahedra, dittigonal symmetry modified from the ideal hexagonal surface symmetry and puckered surfaces instead of the flat planes made up by the basal oxygen atoms of the tetrahedral sheet. The misfit between the lateral dimension of the tetrahedral and octahedral sheets is one of the major... 

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