major forms of AChE (8-10), asymmetric and globular The behavior of the enzyme acetylcholinesterase was studied at forms, which are distinguished on the basis of their quaterthe air/water interface. Surface pressure-area (p-A) isotherms nary structure. Asymmetric forms or collagen-tailed forms and UV-vis spectra recorded at different surface pressures were are characterized by the presence of a collagen-like tail. determined for different salt concentrations in the subphase. The These forms aggregate at low ionic strength in the presence ionic strength of the subphase does not influence the physical of polyanionic compounds (11). The globular forms are properties in consideration; however, the pH of the subphase has heterogeneous. There are amphiphilic and nonamphiphilic a great effect on its surface and optical properties. A subphase at globular forms on the basis of their capacity to associate with pH 6.5 has shown that the enzyme is highly stable, based on the micelles of nondenaturing detergents (8, 12, 13). Globular p-A compression/decompression isotherms. No changes in the area per molecule were observed when the surface pressure was AChE are known to be the most abundant and widely distribmaintained constant at 16 mN/m for a period of 120 min. The uted forms of this enzyme. long-term stability of acetylcholinesterase at the air/water inter-Acetylcholinesterase is considered an important enzyme face was demonstrated for pH 6.5 and a salt concentration of 10 02 among the other biochemical or biological components used M (KCl). The absorption spectra of the monolayer, measured to develop biosensors. Biosensors based on acetylcholinesdirectly at the air/water interface, are considered good evidence terase activities as molecular recognition elements were of the organization of the enzyme molecules. α§ 1997 Academic Press combined with a variety of transducing elements, including