DNA demethylation proteins such as TDG and TET1 (ten-eleven translocation gene protein 1) are useful for a range of applications in DNA demethylation studies such as enzyme kinetics, screening inhibitors, selectivity profiling, ELISA, and protein arrays. DNA demethylation can be passive, active, or both and is defined as the removal of a methyl group from DNA. It is involved in epigenetic reprogramming of genes as well as important disease mechanisms, including tumor progression.