Here's why:

* Folate is a B vitamin that the body needs for various metabolic processes.

* Tetrahydrofolic acid (THF) is the active form of folate.

* Dihydrofolate reductase (DHFR) is an enzyme that converts dihydrofolate (DHF) to THF. This conversion requires the addition of two hydrogen atoms.

* THF is crucial for many metabolic processes, including:

* DNA and RNA synthesis: THF is required for the synthesis of purines and thymine, which are essential building blocks for DNA and RNA.

* Amino acid metabolism: THF is involved in the conversion of one amino acid to another, particularly in the synthesis of methionine from homocysteine.

* Red blood cell production: THF is essential for the production of red blood cells.

Therefore, THF is the major cofactor formed from folate and plays a vital role in many important metabolic processes.