Michaelis-Menton mechanisms

The Michaelis-Menton mechanism (5.51) is the simplest member of a set of series-parallel reactions,... 

Whether A S itself reacts or whether it combines with a gas-phase molecule to yield product, (5.57) is mechanistically equivalent to the Michaelis-Menton mechanism (5.51) it differs from the mechanism (5.49) in that the adsorption process is reversible. The surface sites replace enzyme molecules as catalysts if [A] is too large the surface is saturated. Adapting the arguments that led to (5.53) yields the Langmuir adsorption isotherm which is the fraction of occupied sites 6 = [A S]/5o,... 

Obviously, the reaction steps are not elementary reactions, because the caloric reaction power respectively rate of reaction depends only on the concentration of sulphide, sulphoxid or sulphon but does not depend on the concentration of the reactant H2O2. Such a phenomenon occurs under special conditions when the catalyst first reacts reversibly with one of the reactants (Michaelis Menton mechanism) in the present case ... 

The Michaelis-Menton equation represents a mechanistic model because it is based on an assumed chemical reaction mechanism of how the system behaves. If the system does indeed behave in the assumed manner, then the mechanistic model is adequate for describing the system. If, however, the system does not behave in the assumed manner, then the mechanistic model is inadequate. The only way to determine the adequacy of a model is to carry out experiments to see if the system does behave as the model predicts it will. (The design of such experiments will be discussed in later chapters.) In the present example, if substrate inhibition occurs, the Michaelis-Menton model would probably be found to be inadequate a different mechanistic model would better describe the behavior of the system. 

Enzymes and micelles resemble each other with respect to both structure (e.g., globular proteins and spherical aggregates) and catalytic activity. Probably the most common form of enzyme catalysis follows the mechanism known in biochemistry as Michaelis-Menton kinetics. In this the rate of the reaction increases with increasing substrate concentration, eventually leveling off. According to this mechanism, enzyme E and substrate A first react reversibly to form a complex EA, which then dissociates to form product P and regenerate the enzyme ... 

This mechanism is important for compounds that lack sufficient lipid solubility to move rapidly across the membrane by simple diffusion. A membrane-associated protein is usually involved, specificity, competitive inhibition, and the saturation phenomenon and their kinetics are best described by Michaelis-Menton enzyme kinetic models. Membrane penetration by this mechanism is more rapid than simple diffusion and, in the case of active transport, may proceed beyond the point where concentrations are equal on both... 

A second proposed mechanism of the CCT was based upon a Michaelis—Menton-type mechanism.12 This mechanism is typical of enzymatic catalysis,159 and the rates of CCT have been compared to those of enzymes. It requires the formation of a complex between the catalyst and the monomer (eq 12). The propagating radical then reacts with the complex (eq 13) to transfer a hydrogen atom to the monomer. 

Sudden death is a major factor in cocaine-related fatalities. The mechanism for the cardiotoxicity is not fully understood, but it appears to be poorly predicted from patient to patient. Nevertheless, a rapid immuno-therapeutic response would be essential in treating cocaine-related toxicity, and even catalytic antibodies with low micromolar (M) Michaelis-Menton constant (K ) values may not be fast-acting enough. By comparison, high-affinity anti-drug antibodies typically have dissociation constant (K ) values in the low nanomolar (nM) to high picomolar (pM) range. Therefore, to test the usefulness of catalytic antibodies, it will be important to conduct full dose-response curves with the cocaine catalytic antibodies and to... 

Main (M4), in an excellent review article on cholinesterase inhibitors, discussed the additional complication of substrate inhibition in the above general mechanism. However, in many inhibition studies Michaelis-Menton kinetics are obeyed quite closely. One simple reaction scheme which leads to such kinetics is as follows ... 

The rate equation deduced for this, as well as for other similar mechanisms (W33), has the form of a modified Michaelis-Menton equation for the example given above, the rate equation is... 

A characteristic feature of active transport mechanisms is the existence of a maximal rate, which is ascribed to saturation kinetics analogous to the kinetics for enzymic reactions (Michaelis-Menton). A maximal rate for the transport of taurocholate can be demonstrated in vitro and in vivo (11,14,17, 19). Unfortunately, the interpretation that the observed maximal transport... 

The enantioselective Strecker reaction also succeeds with ketoimines. Thus, a-hranched amino-nitriles [94] and also unnatural amino acids [95] can he obtained hy this method. The precise mechanism of the catalysis is unclear. Kinetic investigations have previously shown, that the turnover reflects a Michaelis-Menton relationship. The imine is bonded reversibly to the catalyst. The addition of hydrogen cyanide is rate-determining. [96]... 

Finally, we end the chapter with a discussion of nature s catalysts enzymes. In fact, we allude to enzymes throughout the chapter. The general manner in which enzymes catalyze reactions is still a matter of debate, and so we present several theories. Our examination of enzymes is in preparation for a few specific enzymatic examples given in Chapters 10 and 11 as highlights for organic reaction mechanisms. Enzymes also provide an excellent setting in which to discuss Michaelis-Menton kinetics, the most common kinetic scenario used for catalysis. We also return to our analysis of the power of changing the thermodynamic reference state to examine reactivity, and show the manner in which an enzyme becomes "perfect". 

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