Binding of anandamide to bovine serum albumin

Abstract

The endocannabinoid anandamide is of lipid nature and may thus bind to albumin in the vascular system, as do fatty acids. The knowledge of the free water-phase concentration of anandamide is essential for the investigations of its transfer from the binding protein to cellular membranes, because a water-phase shuttle of monomers mediates such transfers. We have used our method based upon the use of albumin-filled red cell ghosts as a dispersed biological “reference binder” to measure the water-phase concentrations of anandamide. These concentrations were measured in buffer (pH 7.3) in equilibrium with anandamide bound to BSA inside resealed human red cell membranes at low molar ratios below one. Data were obtained at 0°C, 10°C, 23°C, and 37°C. The equilibrium dissociation constant (Kd) increases with temperature from 6.87 ± 0.53 nM at 0°C to 54.92 ± 1.91 nM at 37°C. Regression analyses of the data suggest that BSA has one high-affinity binding site for anandamide at all four temperatures. The free energy of anandamide binding (ΔG0) is calculated to −43.05 kJ mol−1 with a large enthalpy (ΔH0) contribution of −42.09 kJ mol−1.Anandamide has vasodilator activity, and the binding to albumin may mediate its transport in aqueous compartments.

Keywords

• equilibrium dissociation constant
• resealed red cell membranes
• erythrocyte ghosts
• equilibrium constant of anandamide-albumin complex
• anandamide monomer concentration