Michaelis mimics

Enzyme mimics catalyze reactions by mechanisms which are demonstrably enzyme-like. The minimum requirement is that the reactions concerned should involve an initial binding interaction between the substrate and the catalyst. This gives rise to Michaelis-Menten kinetics reactivity is measured in terms of the familiar parameters kCat and Km and we use E to denote enzyme mimic as well as enzyme. ... 

Thus, the adequate kinetic simulation of methane hydroxidation with hydrogen peroxide on PPFe3+OH/AlSiMg mimic, carried out with the help of the Michaelis-Menten equation, indicates high probability of the monooxygenation mechanism suggested [91]. 

Although neutral methanol and ammonia are more stable in vacuo than their ions, the reaction field is capable of inverting this gap. At 3.0A as the spherical cavity radius, the diionic form becomes more stable. The tetrahedral substrate can approach the dyad to a shorter distance than the planar substrate. The repulsive barrier occurs at distances shorter than 2.5A for the planar, but only at 2.0A for the tetrahedral. The tetrahedral substrate is more stabilized by the reaction field effect than the planar substrate, due to an increase in the in-vacuo dipole moment of the tetrahedral. The reaction field is supposed to mimic the protein surrounding, and it is proposed that the protein stabilizes the diionic form even though the simulation of the reaction field is not sufficient to obtain a realistic interpretation. This study indicates a tendency to tetrahedralization of the model substrate at distances characteristic of the Michaelis-Menten complex formation. The authors believe that this must affect intermolecular interactions of large substrates. 

A minimum requirement for a true enzyme mimic is a binding interaction between two molecules preliminary to the catalytic reaction, indicated by Michaelis-Menten kinetics. Intramolecular systems can support very rapid reactions because we can use synthesis to bring groups together into close and unavoidable proximity. But an enzyme must select and bind its substrate non-covalently in a dynamic equilibrium. The chemistry of... 

Water-soluble cydophanes are also studied as possible catalysts or artificial enzymes the hydrophobic cav-itiy serves as substrate binding site while appended functional groups act as cofactors. The pyruvate oxidase mimic 20 performed remarkably in the oxidation of aromatic aldehydes to the cossesponding esters (MeOH/ H2O), and it displayed Michaelis-Menten kinetics comparable to those of natural enzymes. The encapsulation of cydophanes in dendrimers creates binding sites within microenvironments, resembling those existing in protein superstructures. 

Schematically shown in Fig. 5 is the preparation of an enzyme mimic for the hydrolysis of ester 6 by molecular imprinting. Phosphonate 5 is an analog of the transition state for the alkaline hydrolysis of Ester 4. It was used as a template for polymerization with two equivalents of the binding-site monomer iVJV -diethyl-4-vinyl-benzamidine. Amidinium groups were chosen, because they can interact electrostatically with the side carboxyl-ate group as well as with the anionic transition state of the alkaline hydrolysis, thus achieving substrate recognition and transition-state stabilization. Polymerization of the preassembled binding-site monomer with the template (Fig. 5A) followed by template removal (Fig. 5B) leaves a cavity that acts as transition-state receptor for the ester substrate (Fig. 5C). The imprinted polymer accelerates the hydrolysis of 6 more than 100-fold compared to the reaction at the same pH in buffer solution without the polymer. The reaction kinetics is of the Michaelis-Menten type. A polymer obtained with amidinium benzoate as a control, with a statistical distribution of amidinium groups, is ca. one order of magnitude less active in the hydrolysis of 6.

Miao H.Q., Ishai-Michaeli R., Peretz X, Vlodavsky I., Laminarin sulfate mimics the effects of heparin on smooth muscle cell proliferation and basic fibroblast growth factor-receptor binding and mitogenic activity, J. Cell Physiol, 164(3), 1995,482-490. 

Metallomicellar-catalyzed reactions, inclnding hydrolysis, oxidorednction, and C—C bond formation, might characterize these snpramolecular objects as metalloenzyme mimics that use hydrophobic microenvironment and active centers in constrained domains. In this direction, formal approaches using Michaelis-Menten methods known for enzyme chemistry were applied to kinetics characterization of micellar catalysis. In addition, recent achievements of advanced organometallic reactions such as Heck, Suzuki, and Sonogashira couplings as well as olefin metathesis, directly in water and at room temperature, make the use of surfactants particularly promising to lower the environmental impact, which has become a requirement for the chemical industry in the past years. ... 

Synzyme An enzyme mimic produced by chemical synthesis. To be worthy of the term, the synzyme should exhibit Michaelis-Menten kinetics, significant catalysis, and turnover. See abzyme. 

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