Inhibition plot

Fig. 5.14. Substrate inhibition plots for batch system with top left comer showing the concentration of substrate inhibitor designated by [5 ] (Left Hanes-woolf Right Curve fit).

Figure 2. A representative curve for the 7o inhibition plotted against the concentration of ciguatoxin sample is shown. The vertical lines from each point represent one standard deviation.

As in the simpler inhibition plots the slopes of the lines follow Eqn. 7.28, but the x-axis intercepts are more complex following Eqn. 7.40,... 

Figure 3.1.2 MARA species inhibition plots for testing performed using K2CT2O7...

Fig. 4. Typical inhibition plot of carbofuran onto AChE-based biosensor.

By plotting the inhibition percentage (7%) vs. the pesticide concentration, a typical inhibition plot can be obtained (see Fig. 4). For concentration range see Note 6. 

Lineweaver-Burk plots provide a good illustration of competitive inhibition and pure noncompetitive inhibition (Fig. 9.18). In competitive inhibition, plots of 1/v vs 1/[S] at a series of inhibitor concentrations intersect on the ordinate. Thus, at infinite substrate concentration, or 1/[S] = 0, there is no effect of the inhibitor. In pure noncompetitive inhibition, the inhibitor decreases the velocity even when [S] has been extrapolated to an infinite concentration. However, if the inhibitor has no effect on the binding of the substrate, the is the same for every concentration of inhibitor, and the lines intersect on the abcissa. 

In the event that a particular inhibitor 1 acts by non-competitive inhibition, plots of 1/v versus 1/[S] data obtained at different fixed concentrations of [1] should obey Equation (8.18) and... 

Figure 8. Substrate inhibition. Plot of Uq versus log [A], drawn according to Eq. (11.23), assuming that P, = = 1.

A useful graphical method for the estimation of kinetic parameters in substrate inhibition was described by Marmasse (1963). However, with substrate inhibition plots, even after a successful graphical analysis is completed, one should always fit the data to the appropriate equation with a computer program in order to estimate the kinetic constants. 

Calculated from the equation = I)SJ(S - So), where Kow is the apparent inhibition constant, / is the concentration of inhibitor. So is the slope of the uninhibited line from the competitive inhibition plot, and St is the slope of the inhibited line on the same graph for a particular (/). 

Figure 3.11. Double-inhibition plot of clethodim versus diclofop for wheat acetyl-CoA...

The three reversible mechanisms for enzyme inhibition are distinguished by observing how changing the inhibitor s concentration affects the relationship between the rate of reaction and the concentration of substrate. As shown in figure 13.13, when kinetic data are displayed as a Lineweaver-Burk plot, it is possible to determine which mechanism is in effect. 

Effect of the concentration of inhibitor on the Lineweaver-Burk plots for (a) competitive inhibition, (b) noncompetitive inhibition, and (c) uncompetitive inhibition. The inhibitor s concentration increases in the direction shown by the arrows. 

Competitive and non-eompetitive inhibitions are easily distinguishable from the Lineweaver-Burk plot. In the ease of eompetitive inhibitors, the intereept on tlie 1/Cg axis inereases while tlie intereept of tlie 1/v axis remains unehanged by the addition of the inhibitor. Conversely, with a non-eompetitive inhibitor, only the 1/v axis intereept inereases. The effeet of eompetitive inhibitors ean be reversed by inereasing the substrate eoneentration. Where the enzyme or the enzyme substrate eomplex is made inaetive, a non-eompetitive inhibitor deereases of the enzyme, but remains eonstant. 

FIGURE 14.13 Lineweaver-Bnrk plot of competitive inhibition, showing lines for no I, [I], and 2[I]. Note that when [S] is infinitely large (1/[S] = 0), Enax the same, whether I is present or not. In the presence of I, the negative 3c-intercept = —l/fCjil + U-]/Ki). 

Pure noncompetitive inhibition occurs if Ki = Ki. This situation is relatively uncommon the Lineweaver-Burk plot for such an instance is given in Eigure 14.15. Note that K is unchanged by I (the x-intercept remains the same, with or without I). Note also that Tmax decreases. A similar pattern is seen if the amount of enzyme in the experiment is decreased. Thus, it is as if I lowered [E],... 

FIGURE 14.16 Lineweaver-Burk plot of mixed noncompetitive inhibition. Note that both intercepts and the slope change in the presence of I. (a) When Ki is less than Ki (b) when Ki is greater than Ki. ... 

FIGURE 19.8 At high [ATP], phosphofruc-tokinase (PFK) behaves cooperatively, and the plot of enzyme activity versus [frnctose-6-phos-phate] is sigmoid. High [ATP] thus inhibits PFK, decreasing the enzyme s affinity for frnc-tose-6-phosphate. 

FIGURE 23.12 Inhibition of fructose-1,6-bisphosphatase by fructose-2,6-bisphosphate in the (a) absence and (b) presence of 25 /xM AMP. In (a) and (b), enzyme activity is plotted against substrate (fructose-1,6-bisphosphate) concentration. Concentrations of fructose-2,6-bisphosphate (in fiM) are indicated above each curve, (c) The effect of AMP (0, 10, and 25 fiM) on the inhibition of fructose-1,6-bisphosphatase by fructose-2,6-bisphos-phate. Activity was measured in the presence of 10 /xM fructose-1,6-bisphosphate. 

Lizlovs and Bond reported a molar ratio of 5 1 (SO CI ) for inhibiting pitting in ferritic stainless steels. A plot of critical potential vs. 

Figures 3.12 and 3.13 show the kinetic parameter evaluation of (3.14.5.2) and (3.14.5.4), i.e. jjbm, qm, Kp, and K p. The inhibition phenomena were examined for the growth rate and the rate of CO uptake, respectively. The experimental data followed the quadratic manner as presented in the (3.14.5.2) and (3.14.5.4), respectively. The Sigma Plot 5 was used to...

Plot both sets of data as a Lineweaver-Burk plot for competitive inhibition (see Fig. 

The reading from the plot for the rate without inhibition ... 

---