Serotonin N-acetyltransferase complex. Molecular model of a complex formed between the serotonin N-acetyltransferase enzyme (AANAT) and the zeta isoform structure of a 14-3-3 protein. AANAT is the penultimate enzyme involved in the conversion of serotonin to melatonin in the cells of the pineal gland in the brain. Melatonin modulates the function of the circadian clock, influencing activity and sleep. AANAT is rapidly inactivated when animals are exposed to light at night and therefore controls the rhythm of melatonin production.