The kinetics of norepinephrine-induced stimulation of serotonin N-acetyltransferase in bovine pineal gland.
Fresh pineal explants were cultured in medium 199 containing 0.1 mg/ml of ascorbic acid, 2 mM glutamine, and 0.1% BSA in 95% O2 and 5% CO2 from 1 to 10 h. Norepinephrine (10 micrometers) increased serotonin N-acetyltransferase (NAT) activity from 2.36+ / -0.23 to 6.98+ / -0.46 pmol product produced/mg protein/min (unit), without influencing tryptophan hydroxylase, 5-hydroxytryptophan decarboxylase, monoamine oxidase, or hydroxyindole-O-methyltransferase. Dibutyryl cyclic AMP (1 mM) also stimulated NAT from 1.39+ / -0.12 to 4.33+ / -0.65 U. The norepinephrine-induced stimulation of NAT was blocked by GABA (10 micrometers), by dl-propranolol (20 micrometers), by cycloheximide (30 micrometers), by puromycin (20 micrometers), but not by actinomycin D (10 micrometers). Comparing the kinetics of native and stimulated NAT, the occurred changes in Vmax with regard to both substrates - tryptamine (from 0.885 to 3.44 U) and acetyl CoA (from 3.45 to 9.10 U) - without changes in Km with respect to both tryptamine (Km = 5 micrometers) and acetyl CoA (Km = 50 micrometers). The results of this investigation are interpreted to indicate that the norepinephrine-induced stimulation of NAT may be due to enhanced protein synthesis involving translational or post-translational events. Furthermore, the enhanced protein synthesis is coupled through activation of beta-receptor and cyclic AMP mediated actions in pineal gland. The precise interrelationship between GABA and norepinephrine in mediating and perhaps in controlling the biological events in the bovine pineal gland still awaits clarificaton.
D000123:Acetyltransferases / Q000378:metabolism*; D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000378:metabolism*; D002417:Cattle; D066298:In Vitro Techniques; D007700:Kinetics; D009638:Norepinephrine / Q000494:pharmacology*; D010870:Pineal Gland / Q000187:drug effects* / Q000201:enzymology*; D011943:Receptors, Adrenergic, beta / Q000378:metabolism; D013045:Species Specificity; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D011943:Receptors, Adrenergic, beta; D005680:gamma-Aminobutyric Acid; D000123:Acetyltransferases; D001191:Arylamine N-Acetyltransferase; D009638:Norepinephrine