CONVERSION OF ACETYLCHOLINESTERASE HYDROPHILIC TETRAMERS INTO AMPHIPHILIC DIMERS AND MONOMERS

Exposure of purified hydrophilic tetramers of acetylcholinesterase (AC hE) from fetal bovine serum to various guanidinium chloride (Gdn) conc entrations led to inactive tetramers (2 M Gdn) and dimers (6 M Gdn). T he native tetramers were almost fully monomerized by reduction, a mino r fraction of the released monomers remaining active. Sedimentation an alysis and hydrophobic chromatography showed that the modified tetrame rs, dimers and monomers had amphiphilic properties. Intrinsic fluoresc ence spectra and binding of the amphiphilic probe, 1-anilino-8-naphtha lene sulfonate (ANS), revealed that AChE subunits in the modified tetr amers were in a 'molten globule' structure, the dimers in a denatured state, and the inactive monomers in a 'native-like' structure. These d ata show that AChE subunits possess a flexible conformation, which may be important for generating a full set of molecular forms. In additio n, the behavior of the active monomers with amphiphiles may explain th e interactions of type II AChE forms with membranes. (C) 1996 Academic Press, Inc.