title: Studies on serotonin binding proteins of nerve ending membranes.
abstract: Synaptic membranes were isolated from rat brain homogenates by differential and density gradient centrifugation. Membrane proteins were solubilized by detergent buffer and assayed for serotonin-binding activity by adsorption of free 5-HT on charcoal. When the membrane extract was incubated with serotonin at +4 degrees C for various times, equilibrium was reached within 10 min. With increasing serotonin concentrations the specific part of binding was saturable whereas the non-specific part increased linear with the total 5-HT added. Kinetic analysis of the data revealed two different classes of binding sites with the apparent dissociation constants Kd1 = 5.3X10(-7) M and Kd2 = 1.1X10-5 M. The disociation reaction followed first order kinetics in two steps. The first step was very rapid, the second step proceeded with a half life time t1/2 of 16 min and a dissociation rate constant of k-1 = 7.2X10(-4) s-1. the binding was sensitive to heat and SH-blocking reagents and displaceable by serotonin in excess, d-LSD, and to a lower extent by 5-methoxytryptamine and tryptamine. The significance and localization of the binding sites at the membrane are discussed.
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D008238:Lysergic Acid Diethylamide / Q000494:pharmacology; D008297:Male; D008995:Monoamine Oxidase / Q000032:analysis; D011485:Protein Binding; D011506:Proteins / Q000302:isolation & purification*; D051381:Rats; D011956:Receptors, Cell Surface; D012701:Serotonin / Q000378:metabolism*; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D013570:Synaptic Membranes / Q000187:drug effects / Q000378:metabolism*; D013696:Temperature; D014363:Tryptamines / Q000494:pharmacology
chemical_list: D008024:Ligands; D011506:Proteins; D011956:Receptors, Cell Surface; D013439:Sulfhydryl Reagents; D014363:Tryptamines; D012701:Serotonin; D008238:Lysergic Acid Diethylamide; D008995:Monoamine Oxidase