Evidence for the chemical interaction between 2-mercaptoethanol and tetrahydrofolate.

Ascorbate, 2-mercaptoethanol, and 2,3-dimercaptopropanol (l-3) are used as protective agents to stabilize solutions of tetrahydrofolate and its derivatives. The protective action of these compounds has been thought to be due exclusively to their reducing properties. The spontaneous decomposition of HI-folate to the diazotizable amine, p-aminobenzoylglutamate, has been used to measure quantitatively the reduction of folate with folate reductase (4-6). This method has been criticized as not being quantitative (7). It has been found in this laboratory that when no mercaptoethanol is used during the enzymatic reduction of folate, the amount of diazotizable amine formed is quantitative. On the other hand, when samples of H4-folate prepared by different procedures in the presence of mercaptoethanol were assayed for the content of diazotizable amine, in no case was there a quantitative release of ABG.1 The purpose of the investigation reported here was to clarify this discrepancy. Evidence for a chemical interaction between HI-folate and 2mercaptoethanol is presented. This interaction has a somewhat stabilizing effect on H1-folate. It will also be shown that the rate of spontaneous decomposition of Htfolate to the diazotizable amine is much slower in the case of H1-folate-mercaptoethanol complex.