Effect of various cations on the activity of pineal gland N-acetyltransferase (EC 2.3.1.5) and hydroxyindole-O-methyl transferase (EC 2.1.1.4) in vitro.

The effect of various cations on activity of hydroxyindole-O-methyltransferase (HIOMT) and N-acetyltransferase (NAT) from pineal gland was studied. Copper inhibited both enzymes while calcium and magnesium inhibited HIOMT; the mechanisms of these inhibitions are unknown at this stage. Calcium, magnesium, potassium, and sodium initially stimulated NAT activity, and as the cation concentration increased inhibitory activity was observed. These differential effects on NAT activity may in some way be involved in pineal regulation of cation levels.