Arylalkylamine N-acetyltransferase belongs to the superfamily of acetyltransferases. It is the penultimate enzyme in melatonin synthesis and controls the night/day rhythm in melatonin production in the vertebrate pineal gland. Melatonin is essential for seasonal reproduction, modulates the function of the circadian clock in the suprachiasmatic nucleus, and influences activity and sleep. This enzyme is rapidly inactivated when animals are exposed to light at night. This protein is 80% identical to sheep and rat AA-NAT. Arylalkylamine N-acetyltransferase may contribute a multifactorial genetic diseases such as altered behavior in sleep/wake cycle.