Saturation transfer electron paramagnetic resonance on membrane bound proteins. II-absence of rotational diffusion of the cholinergic receptor protein in torpedo marmorata membrane fragments

Abstract

We have applied the technique of saturation transfer electron paramagnetic resonance to study the rotational diffusion of spin labeled membrane bound cholinergic receptors from Torpedo marmorata. Two different spin labels were used: a spin labeled maleimide derivative which binds covalently to proteins and a long chain spin labeled acylcholine which binds reversibly with a high affinity to the receptor protein. The maleimide spin label has a motion whose rotational correlation time is τ 2 > 10 −3 sec. The long chain spin labeled acylcholine indicates slightly more motion ( τ 2 ⋍ 10 −4 sec ), but the nitroxide in this latter case is probably more loosely bound.