Enzyme-substrate complex attractive forces

The combination of enzyme and substrate is called the enzyme-substrate complex. Although Figure 14.27 shows both the active site and its substrate as having a fixed shape, the active site is often fairly flexible and so may change shape as it binds the substrate. The binding between substrate and active site involves dipole-dipole attractions, hydrogen bonds, and dispersion forces. - (Section 11.2)... 

In some instances, the active center of the enzyme is apparently complementary to the substrate molecule in a strained configuration, enrresponding In the activated complex for ihe reaction catalyzed by the enzyme. The sub-.sirale molecule is attracted to the enzyme, and Ihe forces of alirnclinn cause it to assume the strained stale, with confnr-malional changes that favor the chemical reaction that is. the enzyme decreases the activation energy requirement of the reticiion to such an extent that the reaction proceeds ap-... 

From the standpoint of molecular structure and the quantum mechanical theory of chemical reaction, the only reasonable picture of the catalytic activity of enzymes is that which involves an active region of the surface of the enzyme which is closely complementary in structure not to the substrate molecule itselfi in its normal configuration, but rather to the substrate molecule in a strained configuration, corresponding to the activated complex for the reaction catalyzed by the enzyme the substrate molecule is attracted to the enzyme, and caused by the forces of attraction to assume the strained state which favors the chemical reaction—that is, the activation energy of the reaction is decreased by the enzyme to such an extent as to cause the reaction to proceed at an appreciably greater rate than it would in the absence of the enzyme. This is, I believe, the picture of enzyme activity which is usually accepted. 

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