Histamine-N-Methyltransferase (HNMT)

Histamine N-methyltransferase is one of two enzymes involved in the metabolism of histamine. The other being diamine oxidase. Histamine N-methyltransferase catalyzes the methylation of histamine in the presence of S-adenosylmethionine (SAM) forming N-methylhistamine. HMT is present in most body tissues but is not present in fluid. Histamine N-methyltransferase is encoded by a single gene which has been mapped to chromosome 2.This gene encodes the first enzyme which is found in the cytosol and uses S-adenosyl-L-methionine as the methyl donor. In the mammalian brain, the neurotransmitter activity of histamine is controlled by N(tau)-methylation as diamine oxidase is not found in the central nervous system. A common genetic polymorphism affects the activity levels of this gene product in red blood cells.