A flavoprotein, containing a histidyl(N¦Ð)-(8¦Á)FAD linkage at position 91 in the human protein. An imine intermediate is channeled from the FAD binding site to the 5,6,7,8-tetrahydrofolate binding site through a 40 ? tunnel [7,8,9]. In the absence of 5,6,7,8-tetrahydrofolate the enzyme forms formaldehyde [7,9].
