Abstract

Hydroxyindole O-methyltransferase was purified from bovine pineal, and antiserum to the enzyme was produced in rabbits. Rabbit antiserum precipitated the enzyme from bovine, chicken, rat, and human pineal. The consequences of sympathetic denervation and environmental lighting on hydroxyindole O-methyltransferase were studied in rats. Enzyme activity in the pineals of rats kept in continuous darkness was 2-3 times higher than in rats kept in continuous light. Bilateral superior cervical ganglionectomy reduced the enzyme activity in pineals of rats housed under circadian lighting by about half when compared to normal rats kept under identical lighting conditions. Immunochemical titration indicated that the increase in enzyme activity induced by continuous darkness could be accounted for by an increase in enzyme molecules rather than by a change in enzyme kinetics. These results indicate that the quantity of hydroxyindole O-methyltransferase enzyme protein present in the pineal may be modulated by sympathetic nerve activity, which in turn is modulated by environmental illumination.