KDM1B, also known as LSD2 or Aof1, is an enzyme that plays crucial roles in various biological processes. It has FAD-binding activity and FAD-dependent demethylase activity specific to histone H3-di/monomethyl-lysine-4. It is involved in the regulation of DNA methylation, particularly upstream of spermatogenesis, histone H3-K4 demethylation, and the regulation of gene expression by genetic imprinting.