Some characteristics of the night N-acetyltransferase in the rat pineal gland.

Following light on at night experiments, N-acetyltransferase level declines, at first rapidly and after 20 min more slowly. We partly characterised the night N-acetyltransferase and the residual N-acetyltransferase 20 min after light on. Both enzymes had pH optimum 6.8 and were inactivated thermally in vitro with a half time of 8 min. Pre-treatment with cycloheximide or puromycin did not block the rise in N-acetyltransferase following isoproterenol administration shortly after light on. We propose that night N-acetyltransferase is one enzyme. After light on, the enzyme rapidly deactivates to a less active form. Isoproterenol applied within a short time may partly reactivate the enzyme.