An evaluation of the hydrophobic interactions of chick muscle acetylcholinesterase by charge shift electrophoresis and gradient centrifugation

Abstract The hydrophobic interactions of globular forms of acetylcholinesterase from adult and embryonic chick muscles have been analyzed by sucrose gradient centrifugation and non denaturing polyacrylamide gel electrophoresis. The presence of positively- or negatively-charged detergents influences the electrophoretic migrations of hydrophobic globular forms, whereas the mobility of hydrophilic components is unchanged. We defined an hydrophobicity index (HI) which quantitatively reflects this interaction. Globular forms of acetylcholinesterase were isolated in preparative sucrose gradients of muscle extracts. The G 1 form (5 S) appeared as a single band in electrophoresis, the G 2 form (7 S) under two and the G 4 form (11 S) under three electromorphs. The G 1 and the G 2 forms interacted with detergents: this resulted in a shift in their sedimentation in sucrose gradients upon removal of detergents, and in a modification of their electrophoretic migrations in the presence of charged detergents (HI = 1.0 for G 1 , HI = 1.7 for G 2 ). The G 4 form was heterogenous: one band (G 4f ) did not interact with detergent (HI = 0.1). The other variants (G 4i and G 4s ) were clearly hydrophobic (HI = 0.5 and HI = I respectively). The hydrophilic and hydrophobic variants of the G 4 form however, were not resolved by sedimentation analysis performed in the presence of Triton X100, but their separation was improved in the presence of 10-oleyl-ether. Therefore, the combination of electrophoretic and sedimentation methods, as described in this paper, can be used successfully for subdividing a single molecular form (size isomer defined by hydrodynamic parameters) into several constituents differing by their hydrophobic interactions.