title: [Binding of reversible spin-labeled inhibitors with an butyrylcholinesterase active center].
abstract: The interaction of spin-labeled metacyn, procaine, carbolin and bivalent cations (Ca2+, Co2+, Ni2+) with butyrylcholinesterase (BChE) was studied by ESR and enzyme kinetic methods. The effect of pH, ionic strength and organic solvent was analysed. Spin-labeled metacyn binds at the anionic site of BChE active centre. This complex is stabilized both with coulombic and hydrophobic interactions, ionizing group of active centre with pK 6-7 also affects the binding. Spin-labeled procaine appeared to be enzyme competitive inhibitor (Ki = 4 X 10(-5) M) and is located, most probably, at the same site. Activating effect of Ca2+ ions on BChE was confirmed. Simultaneous application of spin labels and paramagnetic ions demonstrates that cations Co2+ and Ni2+ bind with BChE in the close vicinity of spin-labeled inhibitor site. Paramagnetic cations are located more closely to the cationic part of the inhibitor molecule than to the hydrophobic one, and can be displaced by surplus of Ca2+ ions. The experimental data testify the model of anionic centre which consists of bivalent metal ions and aminoalcyl cationic group subsites and is located in a hydrophobic pocket of the enzyme surface.
mesh_terms: D001665:Binding Sites; D002091:Butyrylcholinesterase / Q000378:metabolism*; D002800:Cholinesterase Inhibitors / Q000378:metabolism*; D002802:Cholinesterases / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D066298:In Vitro Techniques; D007700:Kinetics; D013113:Spin Labels
chemical_list: D002800:Cholinesterase Inhibitors; D013113:Spin Labels; D002091:Butyrylcholinesterase; D002802:Cholinesterases
vernacular_title: Sviazyvanie obratimykh spin-mechenykh ingibitorov s aktivnym tsentrom butirilkholinésterazy.