**3. Main uses of enzyme inhibitors**

The enzyme inhibitors are abundantly original in nature and considered as well as produced as a main part of pharmacology and biochemistry. Natural poisons are frequently enzyme inhibitors which have grown to defend a plant or animal against predators. These natural toxins comprised certain known poisonous compounds. Artificial inhibitors are mostly used as new drugs but also be used as insecticides such as malathion, herbicides, or glyphosate and may be used as disinfectants like triclosan. Some other artificial enzyme inhibitors block acetylcholinesterase, an enzyme which disrupts dejected acetylcholine, and are used as nerve agents in chemical warfare [9]. Pistagremic acid and di-naphthodiospyrol are isolated compounds having enzyme inhibitory activity (**Figure 1**). Coenzyme folic acid is also linked to the anticancer drug methotrexate (**Figure 2**).

**Figure 1.** The chemical structure of natural enzyme inhibitor.

**Figure 2.** (A) Chemical structure of coenzyme folic acid (left side) associated to the anticancer drug methotrexate (right side). (B) The chemical structure of a complex between penicillin G and *Streptomyces* transpeptidase (produced from DB).
