LSD1, a novel and first known lysine-specific histone demethylase, nuclear protein belonging to the flavin monoamine oxidase family with a SWIRM domain, a FAD-binding motif, and an amine oxidase domain. LSD1, a component of several histone deacetylase complexes, is ubiquitously expressed in most of the tissues. A component of the CoREST and other transcriptional co-repressor complexes, LSD1 is known to play an important role in silencing neuronal-specific genes in non-neuronal cells. It is also known to demethylate Lys-4 of histone H3, a specific tag for epigenetic transcriptional activation. Reports suggest that it plays an important role in stimulating androgen-receptor-dependent transcription converting oxygen to hydrogen peroxide (possibly using alternative electron acceptors). Along with nuclear FHL2 it serves as a novel biomarker predictive for prostate cancer.