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Initial reaction velocity

The Michaelis-Menten equation (29) illustrates in mathematical terms the relationship between initial reaction velocity V and substrate concentration [S], shown graphically in Figure 8-3. [Pg.65]

The Michaelis constant is the substrate concentration at which is half the maximal velocity (V 3 /2) attainable at a particular concentration of enzyme. thus has the dimensions of substrate concentration. The dependence of initial reaction velocity on [S] and may be illustrated by evaluating the Michaelis-Menten equation under three conditions. [Pg.65]

Equation (43) states that when [S] is low relative to k, the initial reaction velocity increases as the nth power of[S],... [Pg.67]

It is therefore a fundamental principle in the estimation of every enzyme that the rates measured should be maximal initial reaction velocities, tangents to progress curves at zero time. They really should represent the amount of enzyme protein in the reaction mixture. [Pg.256]

Probably the most important variable to consider in defining optimal conditions or standard conditions is the initial substrate concentration. Most enzymes show a hyperbolic curve as relation between initial reaction velocity and substrate concentration, well known now as the Michaelis-Menten curve. With increasing substrate concentration (S) the velocity (o) rises asymptotically to a maximum value (V) (Fig. 3), according to the expression ... [Pg.256]

Typical output from an absorbance spectrophotometer (dotted line) showing increasing absorbance with time as a result of formation of a colored product. The solid line is a tangent to the initial slope of the (dotted) curve, and the slope of the tangent represents the initial reaction velocity (v) in this cuvette... [Pg.100]

Initial Rate Assumption. The entire reaction progress curve, or at least a substantial portion of it, is typically required to accurately determine the rate constant for a first-order or second-order reaction. Nonetheless, one can frequently estimate the rate constant by measuring the velocity over a brief period (known as the initial rate phase) where only a small amount of reactant is consumed. This leads to a straight-line reaction progress curve see Fig. 6) which is drawn as a tangent to the initial reaction velocity. [Pg.135]

The reduction in concentration of reactants, enzymes, and solute molecules can provide important information about kinetic systems. For example, one can readily differentiate a first-order process from a second-order process by testing whether the period required to reduce a reactant concentration to 50% of its initial value depends on dilution. First-order processes and intramolecular processes should not exhibit any effect on rate by diluting a reactant. In terms of enzyme-catalyzed processes, the Michaelis-Menten equation requires that the initial reaction velocity depends strictly on the concentration of active catalyst. Dilution can also be used to induce dissociation of molecular complexes or to promote depolymerization of certain polymers (such as F-actin and microtubules). [Pg.203]

Figure 1. Plot of the change in product concentration as a function of time of reaction. The initial rate phase corresponds to the early linear region, and a tangent to this early region has a slope corresponding to the initial reaction velocity. (For a detailed description of how one obtains rate constants using the initial rate assumption. See Chemical Kinetics.)... Figure 1. Plot of the change in product concentration as a function of time of reaction. The initial rate phase corresponds to the early linear region, and a tangent to this early region has a slope corresponding to the initial reaction velocity. (For a detailed description of how one obtains rate constants using the initial rate assumption. See Chemical Kinetics.)...
Hyperbolic shape of the enzyme kinetics curve Most enzymes show Michaelis-Menten kinetics (see p. 58), in which the plot of initial reaction velocity, v0, against substrate concentration [S], is hyperbolic (similar in shape to that of the oxygen-dissociation curve of myoglobin, see p. 29). In contrast, allosteric enzymes frequently show a sigmoidal curve (see p. 62) that is similar in shape to the oxygen-dissociation curve of hemoglobin (see p. 29). [Pg.57]

Initial velocity Only initial reaction velocities (v0) are used in the analysis of enzyme reactions. This means that the rate of the reaction is measured as soon as enzyme and substrate are mixed. At that time, the concentration of product is very small and, therefore, the rate of the back reaction from P to S can be ignored. [Pg.59]

Shapes of the kinetics curves for simple and allosteric enzymes Enzymes following Michaelis-Menten kinetics show hyperbolic curves when the initial reaction velocity (v0) of the reaction is plotted against substrate concentration. In contrast, allosteric enzymes generally show sigmoidal curves. [Pg.473]

The initial reaction velocity, vQ, of an enzyme-catalyzed reaction varies with the substrate concentration, [S], as shown in Figure E5.1. The Michaelis-Menten equation has been derived to account for the kinetic properties of enzymes. (Consult a biochemistry textbook for a derivation of this equation and for a discussion of the conditions under which the equation is valid.) The common form of the equation is... [Pg.280]

The Michaelis constant, KM, for an enzyme-substrate interaction has two meanings (1) Ku is the substrate concentration that leads to an initial reaction velocity of V" /2 or, in other words, the substrate concentration that results in the filling of one-half of the enzyme active sites, and (2) KM = (k2 + ki)/kv The second definition of Ku has special significance in certain... [Pg.281]

Inhibition kinetics are included in the second category of assay applications. An earlier discussion outlined the kinetic differentiation between competitive and noncompetitive inhibition. The same experimental conditions that pertain to evaluation of Ku and Vmax hold for A) estimation. A constant level of inhibitor is added to each assay, but the substrate concentration is varied as for Ku determination. In summary, a study of enzyme kinetics is approached by measuring initial reaction velocities under conditions where only one factor (substrate, enzyme, cofactor) is varied and all others are held constant. [Pg.289]

Analysis of three lipase reactions using the titrimetric method illustrates typical reaction progress curves and how, as well as the need, to estimate initial rates by tangential analysis (Fig. C3.1.1). The corresponding initial reaction velocities were 27.5 U/mg forBurkholderia cepacia (formerly, Pseudomonas cepacia) li-... [Pg.381]

Reversible inhibition occurs rapidly in a system which is near its equilibrium point and its extent is dependent on the concentration of enzyme, inhibitor and substrate. It remains constant over the period when the initial reaction velocity studies are performed. In contrast, irreversible inhibition may increase with time. In simple single-substrate enzyme-catalysed reactions there are three main types of inhibition patterns involving reactions following the Michaelis-Menten equation competitive, uncompetitive and non-competitive inhibition. Competitive inhibition occurs when the inhibitor directly competes with the substrate in forming the enzyme complex. Uncompetitive inhibition involves the interaction of the inhibitor with only the enzyme-substrate complex, while non-competitive inhibition occurs when the inhibitor binds to either the enzyme or the enzyme-substrate complex without affecting the binding of the substrate. The kinetic modifications of the Michaelis-Menten equation associated with the various types of inhibition are shown below. The derivation of these equations is shown in Appendix S.S. [Pg.289]

Kinetic Parameters Are Determined by Measuring the Initial Reaction Velocity as a Function of the Substrate Concentration... [Pg.135]

Fig. 2. The relationship between substrate concentration [S] and initial reaction velocity (V0). Fig. 2. The relationship between substrate concentration [S] and initial reaction velocity (V0).
Fig. 4. The relationship between substrate concentration [S] and initial reaction velocity (V0). (a) A direct plot, (b) a Lineweaver-Burk double-reciprocal plot. Fig. 4. The relationship between substrate concentration [S] and initial reaction velocity (V0). (a) A direct plot, (b) a Lineweaver-Burk double-reciprocal plot.
Fig. 3. Plot of initial reaction velocity (V0) against substrate concentration for the allosteric enzyme aspartate transcarbamoylase. Fig. 3. Plot of initial reaction velocity (V0) against substrate concentration for the allosteric enzyme aspartate transcarbamoylase.
In this work we used an aluminium oxide humidity sensor to measure inline the water vapour pressure. We investigated the partitioning of water between SC-CO2 and the enzyme preparation and we determined the influence of water activity on the initial reaction velocity. [Pg.116]

Effect of water activity on initial reaction velocity... [Pg.119]

Figure 5 Initial reaction velocity V[ of the enzymatically catalyzed transesterification of ( )-menthol and isopropenyl acetate in SC-CO2 as a function of water activity aw... Figure 5 Initial reaction velocity V[ of the enzymatically catalyzed transesterification of ( )-menthol and isopropenyl acetate in SC-CO2 as a function of water activity aw...
It must be stressed that the initial reaction velocity should always be measured, as only during the early stages of reaction does proportionality exist between the time and the amount of substrate undergoing reaction. [Pg.288]


See other pages where Initial reaction velocity is mentioned: [Pg.65]    [Pg.49]    [Pg.252]    [Pg.128]    [Pg.248]    [Pg.549]    [Pg.245]    [Pg.236]    [Pg.58]    [Pg.66]    [Pg.281]    [Pg.281]    [Pg.381]    [Pg.576]    [Pg.320]    [Pg.176]    [Pg.844]    [Pg.283]    [Pg.73]   
See also in sourсe #XX -- [ Pg.319 ]




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