A double inhibition kinetic analysis of [3H]-muscimol binding to the gamma-aminobutyric acid receptor on calf brain synaptic membranes. Further studies on the mechanism of homocysteine-induced seizures.
The simultaneous action of pyridoxal 5'-phosphate (PLP) and L-homocysteine on specific [3H]muscimol binding to the gamma-aminobutyric acid receptor on freeze-thawed, Triton-treated calf-brain synaptic membranes was examined kinetically by double inhibition analysis. PLP was found to be a pure inhibitor and L-homocysteine, a partial inhibitor, with respect to [3H]muscimol. Diagnostic analysis of the experimental data showed that the interaction constant (alpha) of the two inhibitors for the free receptor is between 0 and 1, confirming that the two inhibitors act synergistically. Further double inhibition analysis showed that no quaternary receptor-[3H]muscimol-homocysteine-PLP complex is formed although the ternary receptor-homocysteine-PLP complex is present. The localization and relationship of binding groups for both inhibitors is discussed as in their association with the ligand binding site.
D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002417:Cattle; D004357:Drug Synergism; D006710:Homocysteine / Q000378:metabolism / Q000494:pharmacology*; D007700:Kinetics; D046911:Macromolecular Substances; D009118:Muscimol / Q000378:metabolism*; D011732:Pyridoxal Phosphate / Q000378:metabolism / Q000494:pharmacology*; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism*; D012640:Seizures / Q000139:chemically induced; D013570:Synaptic Membranes / Q000378:metabolism*
D046911:Macromolecular Substances; D011963:Receptors, GABA-A; D006710:Homocysteine; D009118:Muscimol; D011732:Pyridoxal Phosphate