Folic acid coenzymes.

@article{Huennekens1958FolicAC,
  title={Folic acid coenzymes.},
  author={Frank M. Huennekens and Mary J Osborn and Hugh R Whiteley},
  journal={Science},
  year={1958},
  volume={128 3316},
  pages={
          120-4
        }
}
The above reactions involving "active formyl" and "active hydroxymethyl" groups, their interconversion, their connections with free HCOOH and HCHO, and their interdigitation with methyl groups are diagrammed in Fig. 1.