ASMT

ASMT is most commonly an enzyme known as acetylserotonin O-methyltransferase, also referred to as HIOMT (hydroxyindole O-methyltransferase). It catalyzes the final step in the biosynthesis of melatonin by methylating N-acetylserotonin to produce melatonin, with S-adenosyl-L-methionine (SAM) serving as the methyl donor. The enzyme is found in a variety of organisms, including vertebrates and plants, where it participates in local melatonin production beyond the central nervous system.

In humans and other animals, ASMT works in conjunction with arylalkylamine N-acetyltransferase (AANAT) to generate melatonin, a hormone involved in regulating circadian rhythms and sleep-wake cycles. The activity and expression of ASMT are influenced by circadian cues and light exposure, contributing to higher melatonin levels at night. In addition to the pineal gland, ASMT or HIOMT can be expressed in other tissues such as the retina, where local melatonin synthesis can occur.

Genetic and biochemical variation in ASMT can affect enzyme efficiency and melatonin production. Consequently, ASMT has been studied in relation to individual differences in sleep traits and circadian biology, with some research examining associations between ASMT gene variants and patterns of melatonin secretion. The enzyme’s activity is a key component of the broader melatonin biosynthesis pathway, which also includes AANAT as an upstream enzyme.

Related terms include the melatonin biosynthesis pathway and the broader family of methyltransferases.