What does the Ki for a competitive inhibitor mean?

What does the Ki for a competitive inhibitor mean?

The inhibitor constant, Ki, is an indication of how potent an inhibitor is; it is the concentration required to produce half maximum inhibition. Plotting 1/v against concentration of inhibitor at each concentration of substrate (the Dixon plot) gives a family of intersecting lines.

Does Ki change with inhibitor concentration?

In general, No. The Ki is the equilibrium dissociation constant of the inhibitor. As long as the mode of inhibition is the same (and the buffer conditions and temperature), the Ki will be the same.

How do you find KI for noncompetitive inhibitors?

Now in case of NC Inhibition, the easiest way to access Ki is to draw the Dixon Plot: 1/v= f([I]). You should be able to draw a straight line between experimental points obtained at a fixed substrate concentration. As a result you should get a set of lines intercepting the x axis at the -Ki value.

What does a lower Ki mean?

The smaller the Ki, the greater the binding affinity and the smaller amount of medication needed in order to inhibit the activity of that enzyme.

What is the difference between Km and Ki?

Ki is a thermodynamic parameter, reporting the true affinity an inhibitor has for binding an enzyme. In contrast, Km is a kinetic parameter, which gives the substrate concentration at which half of the maximum enzymatic reaction rate is attained.

What is the Ki value for the cimetidine inhibition?

Cimetidine and tiotidine were the best inhibitors, with Ki values of 1.1 +/- 0.2 microM and 1.0 +/- 0.0 microM, respectively; both are the first ever described potent and selective inhibitors of the E3 isozyme.

What does higher Ki mean?

If the complex tends to fall apart easily, (high Ki) the enzyme will be free to function more normally. i.e. if the Ki is high, the inhibitory effect will be weak. A small Ki means that the inhibitor is bound tightly, and the amount of active enzyme present will be small so the inhibitory effect will be strong.

How do competitive inhibitors affect Lineweaver–Burk plots?

A competitive inhibitor increases the slope of the line on the Lineweaver–Burk plot, and alters the intercept on the x-axis (since Km is increased), but leaves the intercept on the y- axis unchanged (since Vmax remains constant).

What is the Lineweaver-Burk plot?

In biochemistry, the Lineweaver–Burk plot (or double reciprocal plot) is a graphical representation of the Lineweaver–Burk equation of enzyme kinetics, described by Hans Lineweaver and Dean Burk in 1934. The Lineweaver–Burk plot for inhibited enzymes can be compared to no inhibitor to determine how the inhibitor is competing with the enzyme.

How do you find the km of an enzyme inhibitor?

Vmax and Km can be determined experimentally by measuring V0 at different substrate concentrations. Then a double reciprocal or Lineweaver–Burk plot of 1/V0 against 1/ [S] is made. Reversible enzyme inhibitors can be classified as either competitive or noncompetitive, and can be distinguished via a Lineweaver–Burk plot.

How do uncompetitive inhibitors reduce km?

This is a very rare class of inhibition. An uncompetitive inhibitor binds to the enzyme and enhances the binding of substrate (so reducing Km), but the resultant enzyme-inhibitor-substrate complex only undergoes reaction to form the product slowly, so that Vmax is also reduced: