Constant Michaelis-Menten

Comparison of the ordinary Michaelis-Menten relation with (5.108) shows that the inhibitor did not influence specific growth rate, vmgx, but the Michaelis-Menten constant was affected by the inhibitor and resulted in a constant, known as the apparent Michaelis constant. 

The parameters of the Monod cell growth model are needed i.e. the maximum specific growth rate and the Michaelis-Menten constant are required for a suitable rate equation. Based on the data presented in Tables 10.1 and 10.2, obtain kinetic parameters for... 

Km Michaelis-Menten constant mass transport coefficient... 

When whole cell containing plural enzymes with opposite selectivities and different (Michaelis-Menten constant) values are used, problems of low selectivities occur. If the substrate concentration is decreased, one of the enzymes with low Kra value catalyzes the reaction so that the selectivity can be improved. 

It has been demonstrated spectroscopically that Ce(IV) - and V(V) perchlorates and Ce(IV) nitrate form complexes with alcohols of composition [ROH Ce(IV)] and [ROH V(OH)3]. The agreement between the determined formation constant and the Michaelis-Menten constant for Ce(IV) oxidation is good evidence for the role of these complexes in the oxidation process. The oxidations by Co(iri) and V(V) perchlorates have kinetics... 

Calculated from Michaelis-Menten constants using lipase catalyst. Polymerization with zinc octanoate/butyl alcohol initiator system in bulk. 

The transformation of 8 into 9 was then monitored in 80% aqueous MeOH for substrate concentrations between 0.05 to 0.4 mM, and 12 pM of apparent concentration of 7. Unbuffered nanopure water was always used, as the addition of base accelerates the uncatalyzed oxidation of 8 by air significantly. The catalytic rate constant koat in 80% aqueous MeOH was determined to be 0.13 min. The Michaelis-Menten constant Km was determined to be 0.07 mM, which refers to a higher affinity of the substrate to the metal complex in aqueous methanol than in pure methanol. The rate constant for the spontaneous reaction k on was determined to be 1 X 10 min in 80% aqueous MeOH. The transformation of 8 into 9 is 140,000-fold accelerated over background under these conditions, and is thus more than twice as fast as accelerated than the reaction in pure methanol. 

Ks Michaelis-Menten constant, or half velocity coefficient being numerically equal to the... 

This equation is fundamental to all aspects of the kinetics of enzyme action. The Michaelis-Menten constant, KM, is defined as the concentration of the substrate at which a given enzyme yields one-half of its maximum velocity. is the maximum velocity, which is the rate approached at infinitely high substrate concentration. The Michaelis-Menten equation is the rate equation for a one-substrate enzyme-catalyzed reaction. It provides the quantitative calculation of enzyme characteristics and the analysis for a specific substrate under defined conditions of pH and temperature. KM is a direct measure of the strength of the binding between the enzyme and the substrate. For example, chymotrypsin has a Ku value of 108 mM when glycyltyrosinylglycine is used as its substrate, while the Km value is 2.5 mM when N-20 benzoyltyrosineamide is used as a substrate... 

The question arises as to whether comparisons with protein enzymes are justified. In other words, what can ribozymes really do An important parameter for measuring the efficiency of enzymes is the value of kc-JK. This quotient is derived from the values of two important kinetic parameters kc-Al is a rate constant, also called turnover number, and measures the number of substrate molecules which are converted by one enzyme molecule per unit time (at substrate saturation of the enzyme). Km is the Michaelis-Menten constant it corresponds to the substrate concentration at which the rate of reaction is half its maximum. 

Because the amounts and density of these transporters vary along the gastrointestinal tract, it is necessary to introduce a correction factor for the varying transport rates in the different luminal and enterocyte compartments. Due to the lack of experimental data for the regional distribution, and Michaelis-Menten constants for each drug in Table 18.2, we fitted an intrinsic (concentration-independent) transport rate for each drug to closely approximate the experimental %HIA. This... 

Fig. 20.1. Correlation between the air/water partition coefficient, Kaw, determined from measurements of the surface pressure as a function of drug concentration (Gibbs adsorption isotherm) in buffer solution (50 mM Tris/HCI, containing 114 mM NaCI) at pH 8.0 and the inverse of the Michaelis Menten constant, Km obtained from phosphate release...

The Michaelis-Menten constant defined by Eq. 11, is the equilibrium constant for the dissociation of he ES complex and is inversely related to the affinity of the enzyme for the substrate, therefore, a low KM value reflects high affinity ... 

The problem is that substrate conversions are frequently lower than 10% and thus difficult to detect in most traditional formats. As previously discussed in this chapter, /iPLC allows optimal operation even when working with low substrate conversion (e.g., as low as 1% as described by Wu et al.12). Data obtained allow the calculation of the Michaelis-Menten constant (Km) for ATP. An example of such an evaluation is presented in Figure 6.48 in which the obtained reaction velocities... 

Hydrolysis of methyl hydrocinnamate is catalyzed by the enzyme chymotripsin. Data were obtained at 25 C with pH k7.6 and a constant enzyme concentration. These are of initial reaction rate, mol/1iter-sec, and corresponding initial substrate concentrations. Find the Michaelis-Menten constants. 

From a plot of the internalisation flux against the metal concentration in the bulk solution, it is possible to obtain a value of the Michaelis-Menten constant, Am and a maximum value of the internalisation flux, /max (equation (35)). Under the assumption that kd kml for a nonlimiting diffusive flux, the apparent stability constant for the adsorption at sensitive sites, As, can be calculated from the inverse of the Michaelis-Menten constant (i.e. A 1 = As = kf /kd). The use of thermodynamic constants from flux measurements can be problematic due to both practical and theoretical (see Chapter 4) limitations, including a bias in the values due to nonequilibrium conditions, difficulties in separating bound from free solute or the use of incorrect model assumptions [187,188],... 

Table 3. Representative affinity constants for the binding of metal to transport sites or whole cells/organisms. Ionic strengths and pH values are given for the conditional constants. In the column Comments , information on the method of determination (Km = Michaelis-Menten constant WC = whole-cell titrations) the type of constant (CC = conditional constant IC = intrinsic constant) and special conditions (Cl = competitive inhibitors NICA = nonideal competitive adsorption) are given...

It is perhaps wise to begin by questioning the conceptual simplicity of the uptake process as described by equation (35) and the assumptions given in Section 6.1.2. As discussed above, the Michaelis constant, Km, is determined by steady-state methods and represents a complex function of many rate constants [114,186,281]. For example, in the presence of a diffusion boundary layer, the apparent Michaelis-Menten constant will be too large, due to the depletion of metal near the reactive surface [9,282,283], In this case, a modified flux equation, taking into account a diffusion boundary layer and a first-order carrier-mediated uptake can be taken into account by the Best equation [9] (see Chapter 4 for a discussion of the limitations) or by other similar derivations [282] ... 

It is also interesting to examine how the plateau current varies with the substrate concentration. For simplicity, we assume that the substrate and cosubstrate concentrations are small enough as compared to the Michaelis-Menten constants for saturation effects to be negligible for both reactions. Then, as illustrated in Figure 5.2, the variations of the plateau current are given by... 

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