Cox-1 and Cox-2 enzymes a type of cyclooxygenase enzyme, are responsible for the production of prostaglandins hormones, which can cause inflammation, pain, and fever.
Cox-1 enzymes primarily produce prostaglandins and protect the lining of stomach. Cox-2 are responsible only for production of prostaglandins. The actions of Cox enzymes can be inhibited by NSAIDs, anti-inflammatory drugs.
If a drug inhibits the Cox-1 enzyme, the inner lining of the stomach will not be protected, which will results in ulcers or bleeding. Hence, we need a drug which can specifically inhibit the action of Cox-2 enzyme.
Aspirin is a type of nonsteroidal anti-inflammatory drug which can serve this purpose. Aspirin selectively inhibits the action of Cox-2 enzyme without effecting the Cox-1.
Aspirin is chemically known as Acetylsalicylic Acid (ASA). It has two functional groups: ester and carboxylic acid, attached to the 1st and 2nd carbon respectively on the benzene ring.
Aspirin inhibits the Cox-2 enzyme by irreversible acetylation of -OH group of serine residue present on the active site of Cox enzyme. This results in formation of inactive Cox enzyme.
Acetylation reaction of alcohols can be done by carboxylic acids, acid anhydrides, and ketones, which results in formation of ester group. Here is an example: (see the attached image)
Aspirin works in same manner. Aspirin binds to the Cox enzyme. The -OH group of active Cox- enzyme is replaced by acetyl group of Aspirin resulting in formation of ester group on Cox enzyme and hence inactivating it.