Arylamine N-acetyltransferase and arylalkylamine N-acetyltransferase in the mammalian pineal gland.
Amine N-acetylation in the pineal gland is of special importance because it is the first step in the synthesis of melatonin from serotonin. In the present study the N-acetylation of arylamines and arylalkylamines by homogenates of rat and sheep pineal glands was investigated. The arylamines studied were p-phenetidine and aniline; the arylalkylamines studied were tryptamine, serotonin, 5-methoxytryptamine, 6-fluorotryptamine, and phenylethylamine. These amines were acetylated by pineal homogenates of both species, although marked interspecies differences in apparent Km and Vmax values were found. A series of observations in both species indicate that aromatic amine N-acetylation is catalyzed by two distinct enzymes; one preferentially acetylates arylamines and the other preferentially acetylates arylalkylamines. First, isoproterenol treatment of the rat increased arylalkylamine N-acetylation 100-fold without increasing arylamine N-acetylation. Second, cycloheximide treatment in sheep reduced arylalkylamine N-acetylation at night to one-tenth control values, without altering arylamine N-acetylation. Third, arylamine N-acetyltransferase and arylalkylamine N-acetyltransferase inactivated at different rates at 4 degrees C. Fourth, the two enzymes were resolved by size exclusion chromatography. These results clearly establish that the pineal gland contains an arylamine N-acetyltransferase and a second, independently regulated arylalkylamine N-acetyltransferase which appears to be primarily responsible for the physiological conversion of serotonin to melatonin via the intermediate N-acetylserotonin.
D000107:Acetylation; D000123:Acetyltransferases / Q000378:metabolism*; D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000302:isolation & purification / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D010870:Pineal Gland / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D012756:Sheep; D013379:Substrate Specificity
D003513:Cycloheximide; D000123:Acetyltransferases; D001191:Arylamine N-Acetyltransferase; D007545:Isoproterenol