Significance

In elucidating enzymes catalysis mechanism:Inhibitors are commonly used to probe the chemical and conformational nature of a substrate binding site as part of an effect to elucidate the enzymes catalysis mechanism.
In elucidating metabolic pathways in cells:
1. Enzyme inhibitors are frequently useful as tool to study metabolic pathways. Many of the intermediates in glycolysis and yeast fermentation were discovered largely by the use of inhibitors, blocking the various successive steps and altering the corresponding intermediate to accumulate in sufficient quantities for isolation and identification.

Many enzyme inhibitors are effective chemotherapeutic agent since an unnatural substrate analog can block the action of a specific enzyme in malfunctioning cells.
DIPF (inhibitor of acetylcholine esterase) is used as a nerve poison in military.
Differences between the reversible and the irreversible inhibitors are given in Table 6.7.

Table 6.7 Differences between Reversible and Irreversible inhibitors

Reversible inhibitors	Irreversible inhibitors
The interaction between inhibitor and amino acid of active site is weak.	A covalent bond is formed between the inhibitor and the amino acid of active site. This bond cannot be broken, and so enzyme loses its activity permanently.
The activity returns on merely removing the free inhibitor by dialysis or other means.	The activity does not return on dialysis.
It implies that there is an equilibrium between free I and E. E + I ↔ EI	No such equilibrium between free I and E.
It is independent of time and depends on the I concentration, provided I is stable.	It increases with time reacting complete inhibition even with very dilute inhibitor, provided I is in excess of the amount of E present.
The effectiveness of I is normally expressed by an equilibrium constant (K_i), which is responsible of the enzyme inhibitor affinity.	The effectiveness of I is expressed not by an equilibrium constant but by a velocity constant, which determines the fraction of the E inhibitor in a given period of time by a certain concentration of inhibitor.
Examples are numerous. Action of cyanide on cytochrome c oxidase. Action of malonate on succinate dehydrogenase	Example: Action of cyanide on xanthine oxidase. Action of nerve gases on cholinesterase.