Binding of reversible spin-labeled inhibitors with an butyrylcholinesterase active center

• Published in: Biofizika Vol. 31; no. 5; p. 746
• Main Authors: Dorokhov, K E, Grigorian, G L
• Format: Journal Article
• Language: Russian
• Published: Russia (Federation) 01-09-1986
• Subjects: Binding Sites; Butyrylcholinesterase - metabolism; Cholinesterase Inhibitors - metabolism; Cholinesterases - metabolism; Electron Spin Resonance Spectroscopy; In Vitro Techniques; Kinetics; Spin Labels
• ISSN: 0006-3029

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.