Enzymatic catalysis, mechanisms

Enzymatic catalysis mechanisms may well be considerably more complex than the basic ping-pong mechanism, involving inhibition and hysteresis phenomena. Horseradish peroxidase offers a remarkable example... 

In the course of developing the idea of the enzymatic catalysis mechanism Poltorak [99] stated the uniformity of enzymatic catalysis mechanisms in the framework of suggested notion of linear chain of bond redistribution (linear CBR). Actually, this idea laid the foundation for the catalase reaction mechanism suggested by Poltorak. In this mechanism, owing to composition of linear CBRs he showed the means for effective proton transfer between... 

The kinetic regularities observed lead to consideration of the hydroxylation mechanism in the context of modem ideas about enzymatic catalysis mechanism. 

Developing the ideas of the enzymatic catalysis mechanism, Poltorak [1] formulated a scientific statement about the meeting of chemical mechanisms of homogeneous, heterogeneous and enzymatic catalysis in the framework of the concept of a linear bond redistribution chain... 

T. C. Bruice and S. I Benkovic, Bioorganic Mechanisms, Vol. 1, W. A. Benjamin, New brk, 1966, pp. 1-258 W. P. Jencks, Catalysis in Chemistry and Enzymology, McGraw-Hill, New York, 1969 M. L. Bender, Mechanisms of Homogeneous Catalysis from Protons to Proteins, Wiley-Interscience, New York, 1971 C. Walsh, Enzymatic Reaction Mechanisms, W. H. Freeman, San Francisco, 1979 A. Fersht, Enzyme Structure and Mechanism, 2nd ed., W. H. Freeman, New York, 1985. 

The mechanical behavior of the contractile apparatus of smooth muscle is also very similar to that of striated muscle. So that to the extent that the force-velocity curves reflect the interaction of mechanical force and the rate of enzymatic catalysis, the steps of the chemomechanical transduction cycles in the two muscles are apparently modulated in similar ways. Also relationships between the active isometric force and muscle length are very similar (except as noted above for shorter lengths). 

In this chapter we have seen that enzymatic catalysis is initiated by the reversible interactions of a substrate molecule with the active site of the enzyme to form a non-covalent binary complex. The chemical transformation of the substrate to the product molecule occurs within the context of the enzyme active site subsequent to initial complex formation. We saw that the enormous rate enhancements for enzyme-catalyzed reactions are the result of specific mechanisms that enzymes use to achieve large reductions in the energy of activation associated with attainment of the reaction transition state structure. Stabilization of the reaction transition state in the context of the enzymatic reaction is the key contributor to both enzymatic rate enhancement and substrate specificity. We described several chemical strategies by which enzymes achieve this transition state stabilization. We also saw in this chapter that enzyme reactions are most commonly studied by following the kinetics of these reactions under steady state conditions. We defined three kinetic constants—kai KM, and kcJKM—that can be used to define the efficiency of enzymatic catalysis, and each reports on different portions of the enzymatic reaction pathway. Perturbations... 

Friesner RA, Guallar V (2005) Ab initio quantum chemical and mixed quantum mechanics/molecular mechanics (QM/MM) methods for studying enzymatic catalysis. Annu Rev Phys Chem 56 389 127... 

Electronically excited states of organic molecules, acid-base properties of, 12,131 Energetic tritium and carbon atoms, reactions of, with organic compounds, 2, 201 Enolisation of simple carbonyl compounds and related reactions, 18,1 Entropies of activation and mechanisms of reactions in solution, 1,1 Enzymatic catalysis, physical organic model systems and the problem of, 11, 1 Enzyme action, catalysis of micelles, membranes and other aqueous aggregates as models of, 17. 435... 

The Ping-Pong Mechanism in Homogeneous Enzymatic Catalysis... 

There is a huge literature on enzymes and how they work. Two of the best treatments are A. Eersht, Structure and Mechanism in Protein Science A Guide to Enzyme Catalysis and Protein Folding, W. H. Ereeman, New York, 1999 and P. A. Prey and A. D. Hegeman, Enzymatic Reaction Mechanisms, Oxford University Press, New York, 2007. 

The basic concept is the intuition that, whether homogeneous or heterogeneous, catalysis is primarily a process controlled by a molecular phenomenon since it implies the catalyzed transformation of molecules into other molecules. It follows that on the surface of metals or metal oxides, sulfides, carbides, nitrides usually involved as heterogeneous catalysts, the relevant surface species and the mechanism of their mutual reactions must be of molecular character, as occurs in homogeneous or enzymatic catalysis. 

A systematic study on enzymatic catalysis has revealed that isolated enzymes, from baker s yeast or old yellow enzyme (OYE) termed nitroalkene reductase, can efficiently catalyze the NADPH-linked reduction of nitroalkenes. Eor the OYE-catalyzed reduction of nitrocyclohexene, a catalytic mechanism was proposed in which the nitrocyclohexene is activated by nitro-oxygen hydrogen bonds to the enzymes His-191 and Asn-194 [167, 168]. Inspired by this study Schreiner et al. 

Most cleavable surfactants contain a hydrolyzable bond. Chemical hydrolysis is either acid- or alkaU-catalyzed and many papers discuss the surfactant breakdown in terms of either of these mechanisms, hi the environment, bonds susceptible to hydrolysis are often degraded by enzymatic catalysis, but only few papers dealing with cleavable surfactants have dealt with such processes in vitro. Other approaches that have been taken include incorporation of a bond that can be destroyed by UV irradiation or use of a bond which is cleaved when exposed to ozone. 

Each one of the thousands of chemical reactions of metabolism is catalyzed by an enzyme. Most of these enzymes are proteins, but others are made from RNA (ribonucleic acid). In both cases enzymes are very large molecules with precise three-dimensional structures. The study of the properties of enzymes and of enzymatic catalysis is a third theme of the book. Not only are the chemical mechanisms by which enzymes act of interest but also enzymes are often targets for useful drugs. Incorrectly formed enzymes can result in serious diseases. 

Several broad themes recur frequently in enzymatic reaction mechanisms. Among the most important of these are (1) proximity effects, (2) general-acid and general-base catalysis, (3) electrostatic effects, (4) nucleophilic or electro-philic catalysis by enzymatic functional groups, and... 

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