Histamine N-methyltransferase


Histamine N-methyltransferase is an enzyme that in humans is encoded by the HNMT gene.
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 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, histamine is metabolized by two major pathways: N-methylation via histamine N-methyltransferase and oxidative deamination via diamine oxidase. 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-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.