Topoisomerase I is an enzyme that reduces DNA supercoiling during replication and transcription by creating a reversible nick in one of the two DNA strands.

The enzyme is essential as it relieves supercoiling, thus, preventing tangling (also called catenation) of the DNA during replication, transcription and repair.

Dihydroorotate dehydrogenase is an essential mitochondrial enzyme which catalyzes the fourth synthetic step in the pyrimidine synthesis catalyzing the transformation of dihydroorotate to orotate.

Enzymes are essential catalysts in disease-related pathways which makes them good drug targets due to their distinct, specific substrate binding site.

There are seven types of enzymes based on the reactions they catalyze. These types are: I. Oxidoreductases, II. Transferases, III. Hydrolases, IV. Lyases, V. Isomerases, VI. Ligases and VII. Translocases.

There are four important enzymes measured in blood plasma for the diagnosis and monitoring of tissue damage from heart, liver and pancreatic diseases. These enzymes are Creatine Kinase, Alanine Aminotransferase, Aspartate Aminotransferase and Amylase and Lipase.

DHFR stands for dihydrofolate reductase and it is a critical enzyme catalyzing different steps during DNA synthesis, cell division and growth in human cancer cells and pathogens. For these reasons, DHFR is a critical drug target.

IMPDH stands for inosine monophosphate dehydrogenase. This enzyme catalyzes the rate-limiting oxidation of inosine monophosphate to xanthosine monophosphate. This is an indispensable step in the de novo synthesis of purine nucleobases (especially guanosine monophosphate; GMP).

Farnesyl transferase transfers a 15-carbon farnesyl group to proteins allowing them to be anchored to cell membranes. Inhibitors of this enzyme such as Tipifarnib and Lonafarnib inhibit the modification of proteins blocking their function and, therefore, cell growth.

IDO1 stands for indoleamine-2,3-dioxygenase 1 which is a key immunomodulatory enzyme responsible for immune response suppression. This is achieved by its activity to catabolize tryptophan (an essential amino acid) to kynurenine leading to the accumulation of toxic kynurenine metabolites and the inhibition of T- and NK-cell activity while promoting regulatory T-cell development.