Histamine N-methyltransferase

Histamine N-methyltransferase (HMT, HNMT) is an is_associated_with::enzyme that in humans is encoded by the HNMT is_associated_with::gene.

Histamine N-methyltransferase is one of two enzymes involved in the metabolism of is_associated_with::histamine, the other being is_associated_with::diamine oxidase. Histamine N-methyltransferase catalyzes the methylation of histamine in the presence of is_associated_with::S-adenosylmethionine (SAM) forming N-methylhistamine. HMT is present in most body tissues but is not present in serum. Histamine N-methyltransferase is encoded by a single gene which has been mapped to chromosome 2.

Function
In mammals, is_associated_with::histamine is metabolized by two major pathways: N(tau)-methylation via histamine N-methyltransferase and is_associated_with::oxidative deamination via is_associated_with::diamine oxidase. This gene encodes the first enzyme which is found in the is_associated_with::cytosol and uses is_associated_with::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.