RT Journal Article SR Electronic T1 Adenylate Cyclase from Fasciola hepatica JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 804 OP 819 VO 14 IS 5 A1 JOHN K. NORTHUP A1 TAG E. MANSOUR YR 1978 UL http://molpharm.aspetjournals.org/content/14/5/804.abstract AB Cell-free particles from the liver fluke Fasciola hepatica contain a highly active serotonin stimulated adenylate cyclase. Serotonin (5-HT) stimulates this enzyme 25 to 30-fold over basal activity to activities of 0.80 ± 0.10 nmoles/min·mg protein. Histamine, dopamine, octopamine, epinephrine, and carbachol failed to activate this adenylate cyclase. The kinetics of activation by 5-HT showed apparent negative cooperativity with a Hill coefficient of 0.7. The lower apparent affinity half-maximal activation by 5-HT occurred at 2.1 ± 0.3 µM. Any substitutions on the 5-HT molecule reduced apparent affinity and degree of activation. Apparent affinity and intrinsic activity of indoleamines decreased with decreasing structural similarity to 5-HT. All indoleamines tested compete for the serotonin receptor. Derivatives of lysergic acid also activate this adenylate cyclase, with very high apparent affinity. D-lysergic acid diethylamide (LSD) was the most potent derivative activating maximally about 25% of 5-HT stimulated activity. Half-maximal activation by D-LSD occurred at 40 nM. Activation by LSD was totally stereospecific, with the L-isomer inactive even at 1 mM. Both D- and L-LSD antagonized 5-HT stimulation, but the L-isomer had a 500-fold decreased affinity. 2-bromo LSD (BOL) competitively antagonized 5-HT activation as shown by Schild analysis. BOL also directly inhibited basal (nonactivated) adenylate cyclase. The direct inhibition and antagonism of 5-HT by BOL both involved a single population of receptor sites with the same inhibition constant. This result suggests that BOL inhibits adenylate cyclase by interacting with the 5-HT site and that BOL has a "negative" efficacy for this receptor. The evidence supports a single class of adenylate cyclase regulated only by serotonin receptors.