Table 1

Predicted and observed effect of different transmembrane-signaling models. Further, the spin labels would move further apart after ligand binding; Closer, the spin labels would move closer after ligand binding. The prediction for the piston and rotation models depends on the direction of the piston (in this case described for TM2 moving downward) or rotation (in this case described as a counterclockwise movement of TM2). The data for aspartate receptor with spin labels at positions 39 and 179 are from (9).

Location of spin-labeled residuesPredicted relative position of spin labels Observed relative position of spin labels
Assoc.dissoc.ScissorSeesawPistonRotation
10-207CloserCloserFurtherCloserCloserCloser
10-210CloserCloserFurtherFurtherCloserFurther
10-215CloserCloserFurtherFurtherFurtherFurther
39-179CloserCloserFurtherFurtherFurtherFurther