10-Formyltetrahydrofolate

10-Formyltetrahydrofolate (10-CHO-THF) is a form of tetrahydrofolate that acts as a donor of formyl groups in anabolism. In these reactions 10-CHO-THF is used as a substrate in formyltransferase reactions.

Functions
Two equivalents of 10-CHO-THF are required in purine biosynthesis through the pentose phosphate pathway, where 10-CHO-THF is a substrate for phosphoribosylaminoimidazolecarboxamide formyltransferase.

10-CHO-THF is required for the formylation of methionyl-tRNA formyltransferase to give fMet-tRNA.

Formation from methenyltetrahydrofolate
10-CHO-THF is produced from methylenetetrahydrofolate (CH2H4F) via a two step process. The first step generates 5,10-methenyltetrahydrofolate:


 * CH2H4F +  NAD+  $$\rightleftharpoons$$  CH2H2F  +  NADH  +  H+

In the second step 5,10-methenyltetrahydrofolate undergoes hydrolysis:
 * CH2H2F +  H2O  $$\rightleftharpoons$$  CHO-H4F  +

The latter is equivalently written:
 * 5,10-methenyltetrahydrofolate + H2O $$\rightleftharpoons$$ 10-formyltetrahydrofolate

10-CHO-THF is also produced by the reaction
 * ATP + formate + tetrahydrofolate $$\rightleftharpoons$$ ADP + phosphate + 10-formyltetrahydrofolate

This reaction is catalyzed by formate-tetrahydrofolate ligase.

It can be converted back into tetrahydrofolate (THF) by formyltetrahydrofolate dehydrogenase or THF and formate by formyltetrahydrofolate deformylase.