Apparent Michaelis-Menten constants

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] ... 

The linear response range of the glucose sensors can be estimated from a Michaelis-Menten analysis of the glucose calibration curves. The apparent Michaelis-Menten constant KMapp can be determined from the electrochemical Eadie-Hofstee form of the Michaelis-Menten equation, i = i - KMapp(i/C), where i is the steady-state current, i is the maximum current, and C is the glucose concentration. A plot of i versus i/C (an electrochemical Eadie-Hofstee plot) produces a straight line, and provides both KMapp (-slope) and i (y-intercept). The apparent Michaelis-Menten constant characterizes the enzyme electrode, not the enzyme itself. It provides a measure of the substrate concentration range over which the electrode response is approximately linear. A summary of the KMapp values obtained from this analysis is shown in Table I. 

Table I. Apparent Michaelis-Menten Constants and Maximum Current Densities for Redox Polymer Based Glucose Biosensors(a)...

The following experimental data were obtained based on the amount of pyruvic acid formed in 20 minutes. Calculate the apparent Michaelis-Menten constants. 

Derive the steady state rate expression of Equations (4.38) and (4.39) from the kinetic mechanism of Equation (4.37). What is the apparent Michaelis-Menten constant for this mechanism ... 

Abbreviations GOx-glucose oxidase HRP-horse radish peroxidase PAMAM-poly(arnidoamine) Gn - generation number CPE-carbon paste electrode GCE-glassy carbon electrode ITO-indium-tin oxide CoHCF-cobalt hexacyanoferrate K M - apparent Michaelis-Menten constant LbL-layer-by-layer SAM-self-assembled monolayer... 

Table 3.7. APPARENT MICHAELIS-MENTEN CONSTANTS FOR CATIONIC SUBSTRATES OF MOLYBDENUM HYDROXYLASES [57, 58, 62, 159]...

For GOD, apparent Michaelis-Menten constants K, the substrate concentration at which the reaction velocity is half the maximum velocity, Vmaxl l) ranging from 4 mM to 13 mM have been cited for different immobilization conditions [36]. In excess glucose (i.e, glucose concentrations sufficiently greater ), the rate of hydrogen peroxide generation can be approximated by... 

It follows from (6.105) that for zero order kinetics the rate is proportional to r=kiEi and there is no dependence on pH. At the same time for the first order kinetics at low concentration of H+ the value of the apparent Michaelis-Menten constant is high leading to lower values of ki/Kmapp= =ki/(Km(l+K.2/[H+])), while at high concentration of H+ the value of apparent Michaelis-Menten constant is high once again Km,app=Km(l-i-[H+]/Ki), leading to lower values of ki/Km. w, which means that the kinetics follows a bell-shape behavior. 

The linear measuring range for metabolic sensors depends on the apparent Michaelis-Menten constant (/fMapp) of the immobilized enzyme (not free in solution and approachable from all directions, thus, apparent ). which describes a particular substrate concentration associated with half the maximum rate of the enzyme reaction. The reaction rate of an immobilized receptor enzyme is controlled by the rate of substrate and product diffusion through both the semiper-meable membrane covering the enzyme and the layer of immobilized enzyme itself, resulting in a... 

The influence of substituents on the binding and hydrolysis of several substituted jS-D-xylopyranosides by jS-D-xylosidase from Bacillus pumilus has been investigated. From a comparison of the inhibition constants of the substrates, l-thio-jS-o-xylopyranosides, with the apparent Michaelis-Menten constants of the substrates, it followed that the latter constants are good approximations of the true equilibrium constants. The influence of the substituent on the rate and activation parameters is small. The results are in agreement with, but do not prove, a one-step mechanism without the formation of a glycosyl-enzyme intermediate. 

Characteristic parameters such as the apparent Michaelis-Menten constant and the maximum current under saturating substrate... 

The linear respcmse range of the sensors can be estimated from a Michaelis-Menten analysis of the glucose calibration gra in Figures 4 and 5. The apparent Michaelis-Menten constant Km PP can be determined from the electrochemical Eadie-Hofstee form of the Michaelis-Menten equation (30 ) ... 

Table II. Apparent Michaelis-Menten constants determined from electrochemical Eadie-Hofstee plots...

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