Enzymic activity, effect energies

With the valence bond structures of the exercise, we can try to estimate the effect of the enzyme just in terms of the change in the activation-free energy, correlating A A g with the change in the electrostatic energy of if/2 and i/r3 upon transfer from water to the enzyme-active site. To do this we must first analyze the energetics of the reaction in solution and this is the subject of the next exercise. 

As discussed in the early sections it seems that there are very few effective ways to stabilize the transition state and electrostatic energy appears to be the most effective one. In fact, it is quite likely that any enzymatic reaction which is characterized by a significant rate acceleration (a large AAgf +p) will involve a complimentarity between the electrostatic potential of the enzyme-active site and the change in charges during the reaction (Ref. 10). This point may be examined by the reader in any system he likes to study. 

The collective set of energetic advantages that result from productive substrate binding to the enzyme active site is known as the approximation effect. In concert, these effects can provide an important means of at least partially lowering the activation energy for transition state formation. 

It is believed that these effects derive from salt influences on some process (associated with hydration) involved in establishing activation free energy values for enzymes, although not an active site phenomenon. 

The increase in energy content of an atom, ion, or molecular entity or the process that makes an atom, ion, or molecular entity more active or reactive. In enzymology, activation often refers to processes that result in increased enzyme activity. For example, increasing temperature often can have a positive effect on enzyme activity (See Arrhenius Equation). Other examples of enzyme activation include (1) proteolysis of zymogens (2) alterations in ionic strength (3) alterations due to pH changes (4) activation in cooperative systems (5) lipid or membrane interface activation (6) metal ion effects (7) autocatalysis and (8) covalent modification. 

In enzymic reactions the central ES<= EP transformation is very fast, and the value of kcat is very high. In addition to correctly oriented binding of the substrate at the active center of the enzyme, an effective decrease in activation energy of this reaction step might also be provided by stabilization of the transition state of the substrate molecule in the ES complex. 

However, any compound, even if it is chemically inert, if present at high enough concentrations in biological membranes can change those membranes properties and disrupt their functions. Consequently, membrane-associated processes like photosynthesis, energy transduction, transport in or out of the cell, enzyme activities, transmission of nerve impulses, and so on may deteriorate (see van Wezel and Opperhuizen, 1995 and literature cited therein). Since these effects seem to be primarily dependent on the space that contaminating molecules occupy in the... 

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