Regulation of pineal rhythms in chickens: N-acetyltransferase activity in homogenates

Abstract

In the pineal gland N-acetyltransferase activity (NAT) exhibits a circadian rhythm that can be controlled by environmental lighting. Dark-time NAT is 27 times the levels in the light-time. We studied the properties of NAT of pineal glands of chicks killed in the dark and found: 1. 1. NAT is linear for the first 30 min under assay conditions then levels off. 2. 2. NAT is unstable at 37°C; activity of the enzymes drops to 13–45% (of its value 0°C) in 20 min. Variability in the amount of enzyme activity lost in 20 min can be accounted for by variation in the initial activity. 3. 3. NAT is relatively stable at 0°C over a period of 24 hr. 4. 4. NAT can be protected at 37°C by one of its substrates, acetyl coenzyme A (4 mM). It is also protected by some structural analogs of acetyl coenzyme A (cysteamine, 4 mM; penicillamine, 4 mM) and by some sulfhydryl protecting agents (dithiothreitol, 4 mM; EDTA, 5 mM). The amount of protection by cysteamine is variable over a concentration range of 0.08–800 mM; 8 mM solutions of cysteamine reduce enzyme activity. NAT was lowered by iodoacetate, N-ethylmaleimide and pituitary extract. 5. 5. NAT is protected by dilution.