How do you calculate Ki?

The dissociation constant for the inhibitor is KI = [E][I]/[EI].

How can you calculate the KI for a competitive inhibition?

The inhibition constant Ki in the common case of competitive inhibition can be obtained by simple comparison of progress curves in the presence and in the absence of inhibitor. The difference between the times taken for the concentration of substrate to fall to the same value is used to obtain Ki.

What is the formula for Ki for competitive?

For competitive inhibition,(8.6)ν=Vmax×[S]Km(1+[I]Ki)+[S]where all symbols are as defined in Equation (8.4), and Ki is the inhibitor constant, defined as the concentration of inhibitor required to decrease the Vmax by 50%.

What is a KI value in chemistry?

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.

What is Ki in the Michaelis-Menten equation?

The value Ki is the dissociation constant describing the binding affinity between the inhibitor and the enzyme, while Km is the Michaelis constant in the Michaelis-Menten equation which is used to describe the kinetics of substrate/enzyme binding.

Inhibitor Calculations

What are the units for Ki?

Ki is the inhibition constant, expressed in the same units as I, which you entered into the column titles. Vmax is the maximum enzyme velocity, in the absence of inhibitor, expressed in the same units as Y. Km is the Michaelis-Menten constant, expressed in the same units as X.

What is the KI for an enzyme-inhibitor equivalent to?

For noncompetitive inhibition of enzymes, the Ki of a drug is essentially the same numerical value as the IC50, whereas for competitive and uncompetitive inhibition the Ki is about one-half that of the IC50's numerical value.

What is KI equivalent to?

The data analysis also provides an apparent binding constant, Ki, which is equivalent to Km in standard Michaelis-Menten kinetics.

What is KI in equilibrium?

The Ki inhibition constant also represents a dissociation constant, but more narrowly for the binding of an inhibitor to an enzyme. That is, a ligand whose binding reduces the catalytic activity of the enzyme. The binding equilibrium described by the Ki value depends on the kinetic mechanism of inhibition.

What is the rate constant KI?

k_inact/K_I (sometimes referred to as the covalent efficiency constant) is a second-order rate constant which accounts for both the affinity of the initial reversible encounter complex and the maximal rate of covalent bond formation. It is analogous to the enzyme specificity constant k_cat/K_M in enzyme-substrate kinetics.

How do you calculate Ki with IC50?

Hence, IC50 = E/2 + Ki. Therefore, IC50 is dependent on the enzyme concentration, and is always larger than Ki.

How do you calculate KI from IC50?

In the case of competitive and uncompetitive inhibition, Ki = IC50/ 2. In the case of mixed inhibition, Ki values range from IC50 to IC50/2.

What is KI for noncompetitive inhibition?

The equation for Ki also differs. For noncompetitive inhibitors the Ki = I50 and this relationship is valid with changing [S]. The equations developed require a single substrate, reversible-type inhibitors, and kinetics of the Michaelis-Menten type.

What is the formula for calculation of inhibition?

Percentage of inhibition: (Control OD − (Sample OD/Control OD)) × 100. Sample OD is absorbance of test sample.

How is KI and kinact measured?

A simple approach to measuring kinact/KI was developed that makes use of an irreversible probe for competitive assays run to completion against test compounds. In this system, the kinact/KI value of the test compound is equal to (kinact/KI)probe ×[probe]/IC50.

Is KI an equilibrium constant?

The difference between Kd and Ki is that Kd is a more general, all-encompassing term, whilst Ki is more narrowly used to indicate the dissociation equilibrium constant of the enzyme-inhibitor complex.

Is KI the dissociation constant?

Definition: The inhibitory constant (K_i) is a type of equilibrium dissociation constant (K_d) that represents the equilibrium binding affinity for a ligand that reduces the activity of its binding partner.

What is the equilibrium constant K formula?

For an equilibrium equation aA + bB ⇌ cC + dD, the equilibrium constant, can be found using the formula K = [C]^c[D]^d / [A]^a[B]^b , where K is a constant.

What is a strong Ki value?

Inhibitors with K_i values less than 100 μM were considered potent inhibitors. Inhibitors with K_i values higher than 100 μM were considered nonpotent inhibitors.

Is Ki the same as IC50?

While Ki is a constant value for a given compound with an enzyme, an IC50 is a relative value, whose magnitude depends upon the concentration of sub- strate used in the assay.

What is a small Ki value?

The LOWER the Ki for a particular drug at a particular receptor, the STRONGER its binding affinity for that receptor. This is because the lower Ki means that the drug can occupy 50% of those receptors even when the drug is present in a lower concentration.

What is Ki ratio?

The inhibitory constant (Ki) is the concentration of the inhibitor that is required in order to decrease the maximal rate of the reaction by half. (1,2) Therefore, the smaller the Ki, the smaller amount of medication needed in order to inhibit the activity of that enzyme.

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.

What is KI in molecular docking?

Ensemble docking

Here, the inhibition constant (Ki) was obtained from the binding energy (ΔG) using the formula: Ki = exp(ΔG/RT), where R is the universal gas constant (1.985 × 10⁻³ kcal mol⁻¹ K⁻¹) and T is the temperature (298.15 K).

How do you calculate KI for mixed inhibitors?

The rate equation for mixed inhibition is v = (Vmax * S)/[Km(1 + i/Kic) + S(1 + i/Kiu)]. Note that there are two Ki values Kic for the competitive and Kiu for the uncompetitive parts of inhibition.