Glossary of MOA Terms

From Assay Guidance Wiki

The definitions for these terms were gathered from references

Active site – the specific and precise location on the target responsible for substrate binding and catalysis.

Allosteric activators – an allosteric effector that operates to enhance active site substrate affinity and/or catalysis. (Copeland, Enzymes, pg368)

Allosteric effector – small molecule that can bind to sites other than the enzyme active site and, as a result of binding, induce a conformational change in the enzyme that regulates the affinity and/or catalysis of the active site for its substrate (or other ligands). (Copeland, Enzymes, pg368)

Allosteric repressors – an allosteric effector that operates to diminish active site substrate affinity and/or catalysis. (Copeland, Enzymes, pg368)

Allosteric site – a site on the target, distinct from the active site, where binding events produce an effect on activity through a protein conformational change. (Kenakin, A Pharmacology Primer, p195).

Alpha – typically noted as the ratio, KI’/KI. It reflects the effect of an inhibitor on the affinity of the enzyme for its substrate, and likewise the effect of the substrate on the affinity of the enzyme for the inhibitor. (Copeland, Enzyme, pg268)

Biochemical assay – the in vitro based mechanism used to measure the activity of a biological macromolecule (enzyme).

Cofactor – nonprotein chemical groups required for an enzyme reaction.

Enzyme – protein that acts as a catalyst for specific biochemical reaction, converting specific substrates into chemically distinct products.

Multivariate fitting - Fitting a more than 2 variable model (Example: Response, [Inhibitor], [Substrate]) to all of the data from an MoA experiment using nonlinear regression.

Inhibitor – any compound that reduces the velocity of an enzyme-catalyzed reaction measured in a biochemical assay, as represented by percent inhibition or IC50.

Initial velocity – the initial linear portion of the enzyme reaction when less than 10% of the substrate has been depleted or 10% of the product has formed. (QB Manual, Section IV, pg5)

In vitro – (to be defined later)

Ligand – a molecule that binds to the target. (Kenakin, A Pharmacology Primer, pg 198)

Linearity – A relationship between two variables that is best described by a straight line. In MoA experiments, the amount of product formed should be linear with respect to time.

Substrate – a molecule that binds to the active site of an enzyme target and is chemically modified by the enzyme target to produce a new chemical molecule (product).

Target – a macromolecule or macromolecular complex in a biochemical pathway that is responsible for the disease pathology. (QB manual, Section XII, pg3)

kcat – turnover number representing the maximum number of substrate molecules converted to products per active site per unit time. (Fehrst, Str Mech Prot Sci, pg109)

KI – the affinity of the inhibitor for free enzyme.

KI' – the affinity of the inhibitor for the enzyme-substrate complex.

KM – the concentration of substrate at ½ Vmax, according to the Henri-Michaelis-Menten kinetic model (QB manual, Section IV, pg9)

koff – the off-rate associated with the release of inhibitor from an enzyme-inhibitor complex.

kon – the on-rate associated with the formation of an enzyme-inhibitor complex.