mthfd2l is a member of the tetrahydrofolate dehydrogenase/cyclohydrolase family. this enzyme is expressed in all adult tissues and localizes to the mitochondria, specifically as a peripheral membrane protein in the mitochondrial matrix side of the inner mitochondrial membrane. within the mitochondria, it participates the conversion of folate to formate as part of the mitochondrial pathway for 1-carbon metabolism. in the final step of this pathway, the nadp+-dependent ch2-thf dehydrogenase/ch+-thf cyclohydrolase activity of bifunctional mthfd2l complements the 10-cho-thf synthetase activity of monofunctional mthfd1l. the formate produced via the mitochondrial pathway can contribute to purine and thymidine synthesis and homocysteine remethylation into methionine, as well as be converted into 1-carbon units to fuel the cytoplasmic pathway of folate metabolism.