A 30 μl sample of red blood cell vesicles was mixed with an equal volume of buffer (20 mM Hepes, pH 7.6, 150 mM NaCl, 0.5 % Triton X-100), vortexed and incubated for 5 minutes at 37°C. Subsequently 640 μl sodium phosphate buffer (100 mM Na2PO4, pH 7.6), 50 μl DTNB (5,5'-dithiobis-(2-nitrobenzoic acid), 10 mM in sodium phosphate buffer), and 50 μl acetylthiocholine chloride (12,5 mM in H2O) were added. The reaction took place at room temperature and was measured photometrically at a wavelength of 405 nm according to the Ellmann' method [25].