Enzymatic reactions kinetics

Dumont, T. Barth, D. Corbier, C. Branlant, G. Perrut, M. Enzymatic Reaction Kinetic Comparison in an Organic Solvent and in Supercritical Carbon Dioxide. Biotechnol. Bioeng. 1992, 39, 329-333. 

The advantages of diffusion-control enzyme electrodes over devices controlled by the enzymatic reaction (kinetic-control) are that the linearity is increased above the and the response is no longer dominated by the enzyme reaction. This implies that the enzyme electrode is less sensitive to pH and tern-... 

Then, knowing x, the stability of intermediates and product inhibition both depend on the substituents. So much for details of enzymatic reaction kinetics as depending on details of metaUoprotein structure similar second-order effects are observed in alkyl fluorophos-phates hydrolysis by various Cu(II) complexes containing different chelating N-donors (Wagner-Jauregg et al. 1955) here the rates and turnover numbers increase with Ej (L) of the N-chelators. In the above... 

Almost all works on optimization of a multi-product microbial cell factory focussed on a single objective (e.g., Schmid et al., 2004 Visser et al, 2004 Vital-Lopez et al, 2006). A common feature in these works is the pseudo-stationary assumption. Enzymatic reaction kinetics in a microbial cell factory are reversible and interdependent. In reality, the fluxes due to enzymatic reactions are never stationary. Given the limitations of a model, it is necessary to assume a pseudo-stationary state where some variables fluctuate about an averaged steady state within certain bounds. 

The enzymatic reaction kinetics on the HRP-catalyzed oxidation of p-cresol in aqueous 1,4-dioxane or methanol showed that the cataljdic turnover niunber and Michaelis constant were larger than those in water (235). Numerical and Monte Carlo simulations of the peroxidase-catalyzed polymerization of phenols were demonstrated (236). The simulations predicted the monomer reactivity and polymer molecular weight, leading to synthesis of polymers with specific molecular weight and index. In an aqueous 1,4-dioxane, the formation of monomer aggregate was observed (237), which might elucidate the specific polymerization behaviors in such a medium. 

The Quasi-Equilibrium Approximation Enzymatic Reaction Kinetics... 

T Dumont, D Barth, C Corbier, G Branlant, M Perrut. Enzymatic reaction kinetic Comparison in an organic solvent and in supercritical carbon dioxide. Biotechnol Bioeng 4B(2) 329-333, 1992. 

Although the mechanisms may be complicated and varied, some simple equations can often describe the reaction kinetics of common enzymatic reac tions qiiite well. Each enzyme molecule is considered to have an active site that must first encounter the substrate (reactant) to form a complex so that the enzyme can function. Accordingly, the following reaction scheme is written ... 

A new kinetic enzymatic method for the routine determination of urea in semm has been evaluated. This method is based upon an enzymatic reaction and formation of a coloured complex. The method is based on a modified Berthelot reaction. The reaction was monitored specRophotomebically at 700 nm (t = 25 0.1 °C). The optimal pH value, chosen for the investigation of complex, is 7.8. 

The Michaelis constant is equal to substrate concentration at which the rate of reaction is equal to one-half the maximum rate. The parameters and characterize the enzymatic reactions that are described by Michaelis-Menten kinetics. is dependent on total... 

Saturation kinetics are also called zero-order kinetics or Michaelis-Menten kinetics. The Michaelis-Menten equation is mainly used to characterize the interactions of enzymes and substrates, but it is also widely applied to characterize the elimination of chemical compounds from the body. The substrate concentration that produces half-maximal velocity of an enzymatic reaction, termed value or Michaelis constant, can be determined experimentally by graphing r/, as a function of substrate concentration, [S]. 

There are obviously many reactions that are too fast to investigate by ordinary mixing techniques. Some important examples are proton transfers, enzymatic reactions, and noncovalent complex formation. Prior to the second half of the 20th century, these reactions were referred to as instantaneous because their kinetics could not be studied. It is now possible to measure the rates of such reactions. In Section 4.1 we will find that the fastest reactions have half-lives of the order 10 s, so the fast reaction regime encompasses a much wider range of rates than does the conventional study of kinetics. 

If the velocity of an enzymatic reaction is decreased or inhibited, the kinetics of the reaction obviously have been perturbed. Systematic perturbations are a basic tool of experimental scientists much can be learned about the normal workings of any system by inducing changes in it and then observing the effects of the change. The study of enzyme inhibition has contributed significantly to our understanding of enzymes. 

Michaelis-Menten kinetics, in 1913 L. Michaelis and M. Men ten realized that the rate of an enzymatic reaction... 

The plotting of Dixon plot and its slope re-plot (see 5.9.5.9) is a commonly used graphical method for verification of kinetics mechanisms in a particular enzymatic reaction.9 The proposed kinetic mechanism for the system is valid if the experimental data fit the rate equation given by (5.9.4.4). In this attempt, different sets of experimental data for kinetic resolution of racemic ibuprofen ester by immobilised lipase in EMR were fitted into the rate equation of (5.7.5.6). The Dixon plot is presented in Figure 5.22. 

Enzyme kinetics. Consider a mechanism for an enzymatic reaction in which the E S complex is a dead end ... 

Typical single-substrate enzymatic reactions can be described by the kinetic scheme (see Refs. 1 and 2 for more extensive discussions). 

Chapter 10 begins a more detailed treatment of heterogeneous reactors. This chapter continues the use of pseudohomogeneous models for steady-state, packed-bed reactors, but derives expressions for the reaction rate that reflect the underlying kinetics of surface-catalyzed reactions. The kinetic models are site-competition models that apply to a variety of catalytic systems, including the enzymatic reactions treated in Chapter 12. Here in Chapter 10, the example system is a solid-catalyzed gas reaction that is typical of the traditional chemical industry. A few important examples are listed here ... 

FIGURE 12.1 Effects of substrate (reactant) concentration on the rate of enzymatic reactions (a) simple Michaelis-Menten kinetics (b) substrate inhibition (c) substrate activation. 

Second-order enzymatic reactions require two adsorption events at the same site. For the reaction A + B — P, there may be a compulsory order of adsorption (e.g., first A, then B) or the two reactants may adsorb in a random order. Different assumptions lead to slightly different kinetic expressions, but a general form with theoretical underpinnings is... 

CK catalyzes the reversible phosphorylation of creatine in the presence of ATP and magnesium. When creatine phosphate is the substrate, the resulting creatine can be measured as the ninhydrin fluorescent compound, as in the continuous flow Auto Analyzer method. Kinetic methods based on coupled enzymatic reactions are also popular. Tanzer and Gilvarg (40) developed a kinetic method using the two exogenous enzymes pyruvate kinase and lactate dehydrogenase to measure the CK rate by following the oxidation of NADH. In this procedure the main reaction is run in a less favorable direction. 

The simplest method of coupling enzymatic reactions to electrochemical detection is to monitor an off-line reaction using FIAEC or LCEC. The enzymatic reaction is carried out in a test tube under controlled conditions with aliquots being taken at timed intervals. These aliquots are then analyzed for the electroactive product and the enzyme activity in the sample calculated from the generated kinetic information. 

Coles, B., Wilson, I. and Wardman, P. (1988). The spontaneous and enzymatic reaction of N-acetyl-/>-benzoquinone imine with glutathione, a stopped flow kinetic study. Arch. Biochem. Biophys. 264, 253-260. 

There have been many papers reporting studies on the influence of structure and conditions of the medium. Specifically, the kinetic behavior of enzymatic reactions in two-phase media was probed [7,25,27,63]. The reaction localization and the interaction between mass transfer and metabolism in compartmentalized media are interesting phenomena. Their study in the laboratory are useful for optimizing the operating conditions of bioreactors in a preparative scale. In addition, they also help to understand better the behavior of enzymatic systems in vivo. 

Furthermore, in the system with coupled lipase and lipoxygenase, the production rate of HP is governed by the first enzymatic reaction and mass transfer. When TL,- is small (0 to 1 mM equiv. 3 mM LA), the kinetic curve has a sigmoid shape due to surface active properties of LA and HP [25]. Hydrolysis of TL and the increase of LA favor the transfer of LA. Such a transfer allows the lipoxygenase reaction to progress. Since lipox-ygenation consumes LA and produces HP, catalysis and transfer demonstrates a reciprocal influence. 

The differences in the rate constant for the water reaction and the catalyzed reactions reside in the mole fraction of substrate present as near attack conformers (NACs).171 These results and knowledge of the importance of transition-state stabilization in other cases support a proposal that enzymes utilize both NAC and transition-state stabilization in the mix required for the most efficient catalysis. Using a combined QM/MM Monte Carlo/free-energy perturbation (MC/FEP) method, 82%, 57%, and 1% of chorismate conformers were found to be NAC structures (NACs) in water, methanol, and the gas phase, respectively.172 The fact that the reaction occurred faster in water than in methanol was attributed to greater stabilization of the TS in water by specific interactions with first-shell solvent molecules. The Claisen rearrangements of chorismate in water and at the active site of E. coli chorismate mutase have been compared.173 It follows that the efficiency of formation of NAC (7.8 kcal/mol) at the active site provides approximately 90% of the kinetic advantage of the enzymatic reaction as compared with the water reaction. 

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