TY - JOUR T1 - Metal and Metal-ATP Interactions with Human Platelet Adenylate Cyclase: Effects of <em>Alpha</em> Adrenergic Inhibition JF - Molecular Pharmacology JO - Mol Pharmacol SP - 1073 LP - 1078 VL - 14 IS - 6 AU - KARL H. JAKOBS AU - WILHELM SAUR AU - GÜNTER SCHULTZ Y1 - 1978/11/01 UR - http://molpharm.aspetjournals.org/content/14/6/1073.abstract N2 - In human platelet lysates, metal and metal-ATP interactions with adenylate cyclase have been studied, using Mg++ as divalent cation. The kinetic pattern followed Michaelis-Menten kinetics and conformed to a bireactant mechanism in which free metal served as a requisite activator. The alpha adrenergic component of epinephrine (20 µM) reduced Vmax of the enzyme by about 60% without changing the apparent affinities for the substrate, Mg-ATP, and the activator, free Mg++. The inhibition was partial and noncompetitive, with an apparent KI value of 2 µM for epinephrine. ACKNOWLEDGMENTS We are grateful to Ms. Gabriele Gabel for superb technical assistance and to Dr. Roger A. Johnson for his helpful advice during the kinetic experiments. ER -