Links between folate metabolism and formaldehyde. The genotoxin formaldehyde and the folate-dependent one-carbon cycle are intrinsically linked. THF (as well as dihydrofolate and 5,10-methyleneTHF) are susceptible to oxidative degradation to release its constituents: pterine, para-aminobenzoylglutamate (pABG), and formaldehyde. Formaldehyde can directly damage DNA through the formation of a number of DNA lesions. THF can sequester formaldehyde to form 5,10-methyleneTHF.