ARYLAMINE AND ARYLALKYLAMINE N-ACETYLTRANSFERASES IN RETINA, PINEAL-GLAND, BRAIN AND LIVER OF CHICKS - A COMPARATIVE-STUDY

Regulation of arylamine N-acetyltransferase (A-NAT) and arylalkylamine N-acetyltransferase (AA-NAT) was examined in retina, pineal gland, br ain and liver of chicks. Enzyme activities were determined using as su bstrates p-phenetidine and procainamide for A-NAT, tryptamine and phen ethylamine for AA-NAT. The activity of A-NAT in all tissues studied do es not appear to be regulated by a light-dark cycle. On the other hand , AA-NAT showed distinct light-dark dependent changes (with high Value s at night) in the retina and pineal gland, but not in brain and liver . The nocturnal increase of retinal and pineal AA-NAT activity was pre vented by cycloheximide; the drug did not affect A-NAT activity in the se tissues. Treatment of light-adapted chicks with aminophylline signi ficantly increased AA-NAT activity of the retina and pineal gland, wit hout altering the enzyme activity in brain and liver. In these animals , the activity of A-NAT (procainamide) did not change in any tissue st udied, whereas the enzyme activity measured using p-phenetidine as a s ubstrate did decrease but only in the retina. A similar pattern of cha nges in retinal A-NAT and AA-NAT activities was observed after intraoc ular injection of d,b-cAMP. The rate of inactivation at 4 degrees C wa s significantly slower for AA-NAT than A-NAT. NATs from brain and live r displayed the highest and lowest, respectively, lability in the cold . The results indicate that the chick retina contains both A-NAT and A A-NAT. The two enzymes have distinct characteristics and the regulatio n of their activities is different. The retinal A-NAT is similar to A- NAT present in other tested tissues; however, AA-NAT can be induced at night only in the retina and pineal gland. It is suggested that there are two forms of retinal A-NAT, and that, under specified conditions, the activity of one form (A-NAT; p-pheneditine) may be regulated in a n opposite manner to AA-NAT activity.