[Binding of reversible spin-labeled inhibitors with an butyrylcholinesterase active center]. / Sviazyvanie obratimykh spin-mechenykh ingibitorov s aktivnym tsentrom butirilkholinésterazy.

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.

[Interaction of spin-labeled methacyne analog with butyrylcholinesterase]. / O vzaimodeistvii spin-mechenogo analoga metatsina s butirilkholinésterazoi.

Interaction between spin-labeled methacyne (I) and butyrylcholinesterase (BChE) was studied by ESR and enzyme kinetic methods. The compound (I) was shown to be a competitive reversible inhibitor, the value of Ki appeared to be 1.3 X 10(-5) M. Insertion of nitroxyl fragment in the methacyne molecule results in a two-fold increase of its inhibitory activity. The ESR spectrum of the enzyme-inhibitor complex was registered. This complex dissociates under the action of eserine, tetramethylammonium and hexamethonium. Scatchard plot reveals two different types of binding sites with Kdiss values 1.5 X 10(-5) M and 2.6 X 10(-4) M. One type of binding sites is identified as the enzyme active centre. The restricted motion of (I) in complex with BChE proves the assumption that the enzyme active centre is located in the split of macromolecule surface.