Yonetani-Theorell plot

Figure 3.11 Yonetani-Theorell plots for determining mutual exclusivity of two inhibitors. (A) Plot for two inhibitors that bind in a mutually exclusive fashion to a target enzyme (B) plot for two inhibitors that bind independently (y = 1) to the same target enzyme.

Yonetani-Theorell plot will converge at the jc-axis. When y is finite but not unity, the lines intersect above or below the jc-axis. For any Yonetani-Theorell plot that displays intersecting lines, the jc-axis value (i.e.,. /]) that corresponds to the point of intersection will yield the value of -jKj. If K and Kt have been determined independently, one can easily calculate the value of y from the point of intersection in a Yonetani-Theorell plot. 

The topologically defined region(s) on an enzyme responsible for the binding of substrate(s), coenzymes, metal ions, and protons that directly participate in the chemical transformation catalyzed by an enzyme, ribo-zyme, or catalytic antibody. Active sites need not be part of the same protein subunit, and covalently bound intermediates may interact with several regions on different subunits of a multisubunit enzyme complex. See Lambda (A) Isomers of Metal Ion-Nucleotide Complexes Lock and Key Model of Enzyme Action Low-Barrier Hydrogen Bonds Role in Catalysis Yaga-Ozav /a Plot Yonetani-Theorell Plot Induced-Fit Model Allosteric Interaction... 

YAGA-OZAWA PLOT YONETANI-THEORELL PLOT INDUCED FIT MODEL... 

A popular version of the Dixon plot in Fig. 7 is the Yonetani-Theorell plot, in which the ratios of inhibited and uninhibited reaction rates are plotted against increasing concentrations of one inhibitor, in the presence of a constant concentration of the other. This method was apphed for analysis of the competitive inhibition of hver alcohol dehydrogenase by ADP and o-phenanUiroline (Yonetani Theorell, 1964). 

A graphical procedure for analyzing effects of two competitive inhibitors at the active site of an enzyme Vq/vi is plotted as a function of ([Ii] + [I2]) where Vq is the initial-rate velocity in the absence of an inhibitor(s), Vi is the velocity in the presence of the inhibitor(s), and [ii] and [I2] are the two inhibitor concentrations . If there are no interactions between the two inhibitors, then a straight line will be obtained if there is an interaction at the active site, curvature will be observed. See Yonetani-Theorell Treatment... 

To determine the value of y, Yonetani and Theorell suggest measuring reaction velocity at several fixed concentrations of one inhibitor while titrating the second inhibitor. The reciprocal of velocity (l/v0) is then plotted as a function of concentration for the titrated inhibitor (Figure 3.11). If the two compounds are binding in a mutually exclusive fashion, this type of plot results in a series of parallel lines (Figure 3.11A). If the two compounds bind independently (y = 1) the lines in the... 

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