The Biosynthesis of Thymidylic Acid. v. Hydrogen Isotope Studies with Dihydrofolic Reductase and Thymidylate Synthetase.

The first experiments on hydrogen transfer in the thymidylate synthetase reaction (Equation 1) were reported by Friedkin (2, 3). Borohydride labeled with tritium was used to reduce folic acid to tritium-labeled tetrahydrofolate which was then treated with formaldehyde to yield the 5, lo-methylene derivative. When the latter compound was used as substrate for thymidylate synthetase (prepared from Escherichiu coli), tritium was incorporated into the methyl group of the thymidylate formed.