Histamine N-methyltransferase (HNMT) is an enzyme that is responsible for breaking down histamine, by adding a methyl group to it (a process known as methylation).
Key points:
Function: Its primary function is to metabolize histamine, leading to its inactivation.
Methylation of Histamine: Histamine is methylated by HNMT through the transfer of a methyl group from S-adenosylmethionine (SAM) to histamine. This methylation converts histamine into N-methylhistamine, which is a less biologically active form.
Tissue Distribution: HNMT is an enzyme found in various tissues, including the liver, kidney, and central nervous system. The highest levels are found in the liver, where the majority of systemic histamine metabolism takes place.
Genetic Variation: Genetic variations in the HNMT gene can influence the activity of the enzyme.
Role in Allergic Responses: While histamine is involved in allergic responses, HNMT is not the primary enzyme responsible for histamine release. The main enzyme involved in histamine release is histidine decarboxylase.
Clinical Implications: Abnormalities in histamine metabolism, including variations in HNMT activity, have been associated with certain conditions, including allergic disorders and neurological disorders.
Drug Metabolism: HNMT is also involved in the metabolism of certain drugs, as some drugs share structural similarities with histamine. The enzyme helps in breaking down these drugs, contributing to their elimination from the body.