PINEAL SEROTONIN <i>N</i>‐ACETYLTRANSFERASE ACTIVITY: PROTECTION OF STIMULATED ACTIVITY BY ACETYL‐CoA AND RELATED COMPOUNDS

Abstract

Abstract —Rat pineal serotonin N —acetyltransferase activity increases 30–70‐fold at night in the dark and then decreases rapidly when animals are exposed to light. Activity of the enzyme is also stimulated by l ‐norepinephrine in organ culture. When homogenates of glands stimulated by dark in vivo or NE in vitro are incubated at 37°C, enzyme activity will also rapidly decrease. This decrease can be prevented by one of the cosubstrates of the enzyme, acetyl–CoA. Protection can also be conferred by cysteamine (β‐mercaptoethylamine, HS–CH 2 –CH 2 –NH 2 ) which is the terminal portion of the CoA molecule. This protection mechanism could be involved in the physiological control of enzyme activity.