Abstract
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.
Highlights
Amine N-acetylation in the pineal gland is of special rat indicate that pineal and liver N-acetyltransferase differ in importance because it is the first step in the synthesisspecificity (6, 7), stability (8), inhibition by melatonin (9), of melatonin from serotonin
Arylamine N-acetyltransferase andstudy the N-acetylation of arylamines and arylalkylamines by arylalkylamine N-acetyltransferase inactivateadt dif- rat and sheep pineal homogenates
The K,(app) and V,(app) values obtained with 3 other indoleamines were generally similar to those obtainedusing tryptamine (Table I); thserotonin value agrees with a previous report ( 7 )
Summary
The kinetic characteristics of amine-acetylation were studied using five arylalkylamines and two arylamines (Table I). Acetylation of Arylulkylumines-The pineal supernatant from isoproterenol-treated rats appears to contain an enzyme which has a K,(app) for tryptamine of 1.7-4.5 mM, in agreement with previous studies ( 7 ) .A similar value (3.4 mM) was found after a 15-fold enrichment of this enzyme on a Sepharose-cystamine column. Studies on sheep pineals obtained during the day or night indicated there were no daylnight differences in the K,(app) for tryptamine, serotonin, and AcCoA. Acetylation of Arylamines-Rat and sheep pineal supernatants prepared from glands obtained during the day or night acetylate p-phenetidine and aniline. Arylamine, acetylation withrat and sheep pineal supernatant preparations The K,(app) for acetyl-coA with p-phenetidine was 5.9 mM in the rat and 1.6 mM in the sheep preparations These values are 20-40-fold greater than the K,(app) for AcCoA measured with tryptamine. Size exclusion chromatography of the 100,000 X g supernatant from isoproterenol-treated rat pineal glands
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
