(6S)-5,6,7,8-tetrahydrofolate + formaldehyde => (6R)-5,10-methylene-5,6,7,8-tetrahydrofolate + H2O
(6s)-5,6,7,8-tetrahydrofolate + formaldehyde => (6r)-5,10-methylene-5,6,7,8-tetrahydrofolate + h2o
(6S)-5,6,7,8-tetrahydrofolate + formaldehyde => (6R)-5,10-methylene-5,6,7,8-tetrahydrofolate + H2O
(6s)-5,6,7,8-tetrahydrofolate + formaldehyde => (6r)-5,10-methylene-5,6,7,8-tetrahydrofolate + h2o