In enzyme reactions

Wolfenden, R., 1972. Analogue approaches to die structure of the transition state in enzyme reactions. Accounts of Chemical Research 5 10-18. 

Ghisla, S., Entsch, H., Massey, V., and Husein, M. (1977). On the structure of flavin-oxygen intermediates involved in enzymic reactions. Eur. J. Biochem. 76 139-148. 

The reaction mechanisms for reversible reactions are slightly different. In the above section, the second part of the reaction that leads to product was irreversible. However, if all the steps in enzyme reactions were reversible, the resulting rates may be affected. 

Strictly speaking, the conformations and relative geometries of the reactants must be known over the entire reaction coordinate moreover, there are indications that the transition states in enzyme reactions, which often have very different preferred conformations from those of the bound substrates, may be more tightly bound to the enzyme than either the starting materials or the products (1). 

The Qxo, or temperature coefficient, is the factor by which the rate of a biologic process increases for a 10 °C increase in temperature. For the temperatures over which enzymes are stable, the rates of most biologic processes typically double for a 10 °C rise in temperature (Qjo = 2). Changes in the rates of enzyme-catalyzed reactions that accompany a rise or fall in body temperature constitute a prominent survival feature for cold-blooded life forms such as lizards or fish, whose body temperatures are dictated by the external environment. However, for mammals and other homeothermic organisms, changes in enzyme reaction rates with temperature assume physiologic importance only in circumstances such as fever or hypothermia. 

Unlike reactions involving microorganisms, in enzyme reactions the catalytic agent (the enzyme) does not reproduce itself. An example in the use of enzymes is the isomerization of glucose to fructose ... 

The importance of hydrophobic binding interactions in facilitating catalysis in enzyme reactions is well known. The impact of this phenomenon in the action of synthetic polymer catalysts for reactions such as described above is significant. A full investigation of a variety of monomeric and polymeric catalysts with nucleophilic sites is currently underway. They are being used to study the effect of polymer structure and morphology on catalytic activity in transacylation and other reactions. 

A major question has been that of bifunctional catalysis . For example, if a micelle contains both nucleophilic groups and groups which can transfer protons one might hope to achieve high rates of deacylation by having concerted nucleophilic attack and proton transfer (Scheme 6). Such concerted processes are well established in enzymic reactions, but evidence in... 

A coenzyme is an organic compound that activates the primary enzyme to a catalytically active form. A coenzyme may act as a cofactor (see footnote 2), but the converse is not necessarily true. For example, the coenzyme nicotinamide adenine dinucleotide, in either its oxidized or reduced forms (NAD+ or NADH), often participates as a cofactor in enzyme reactions. 

Figure 2.5 Plot between TIME (P) Vs time in Enzymic Reaction. ...

Rose n> has distinguished between substrate specificity (which may not seem stereospecific) and reaction stereospecificity (which is always present in enzyme reactions) in a thought-provoking essay, in which he also describes the usefulness of stereospecificity generally in studying enzyme mechanisms. He has done this so much better than I could, that I will not try to add to this subject. He has also pointed out how stereo-specificity may be useful in the study of evolution. This is a subject I would like to amplify. The less we know, the more we say. Nevertheless,... 

Solvent Kinetic Isotope Effects in Enzyme Reactions (See Also Section 11.4)... 

Solvent Kinetic Isotope Effects in Enzyme Reactions... 

Observations that do not definitively indicate tunneling 70 Observations that likely indicate tunneling 71 Models for tunneling in enzyme reactions 72 Bell tunneling 72... 

Table 2 contains, in reverse chronological order, detailed information about the results of 15 experimental studies of tunneling in enzymic reactions, conducted in the last hve years. These examples will be used to explore the range of evidence, reaction types, enzymes, and concepts currently under study. Other progress made during the preceding decade will be referred to in the discussion of these examples and has been treated in a number of reviews. °... 

Klinman, J.P. (1991). Hydrogen tunneling and coupled motion in enzyme reactions. In Enzyme Mechanism from Isotope Effects, Cook, P.F. (ed.), pp. 127-148. CRC Press, Boca Raton... 

This topic is related to the role that hydrogen bonds play in enzymic reactions and recent work in this area is covered in Section 5. It will be seen that hydrogen bonds are involved in the stabilization of the enzyme, the enzyme-substrate complex, and the transition state for the reaction. 

Intramolecular reactions often differ from their intermolecular counterparts in the exceptionally high rates that are observed and some reactions can occur intramolecularly that are impossible between separate molecules. Because of the importance of intramolecular catalysis, the subject has been reviewed frequently, particularly with reference to its connection with enzymic catalysis (Page, 1973, 1984 Fife, 1975 Jencks, 1975 Kirby, 1980 Fersht, 1985 Menger, 1985). The present coverage is limited to examples of intramolecular catalysis that owe some of their efficiency to intramolecular hydrogen bonding. The role that hydrogen bonds play in enzymic reactions is discussed in Section 5. 

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