THE CIRCULAR DICHROISM OF SYNAPTOSOMAL MEMBRANES: STUDIES OF INTERACTIONS WITH NEUROPHARMACOLOGICAL AGENTS1

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Abstract
The circular dichroic spectrum of synaptosomal membranes was highly reproducible and qualitatively similar to that of erythrocyte membranes. The spectrum exhibited a minimum at 224 nm, a shoulder at 212 nm and a maximum at 195 nm. The mean molar ellipticity at the maximum and minimum was approximately +8000 and –8000 respectively. The protein components were the dominant source of the CD signal. Quantitative estimates showed negligible contributions to the spectrum from cholesterol, phosphatidyl serine and TV‐acyl sugars. Phospholine iodide, eserine, decamethonium, tetramethyl ammonium chloride and acetylcholine at concentrations of 10‐3 and 10‐4M did not produce detectable perturbations of the membrane circular dichroism. The circular dichroic spectrum of d‐tubocurarine exhibited a maximum at 198 nm and a minimum at 212 nm. Addition of d‐tubocurarine to membrane suspensions in the cuvette yielded a complex spectrum representing the result of a simple additive combination of the circular dichroic spectra of d‐tubocurarine and the membranes. However, preincubation of the membranes with 3 x 10‐3m d‐tubocurarine at 0‐4°C for 5‐10 min followed by sedimentation, several washes and resuspension resulted in a circular dichroic spectrum which appeared to involve no change in the membrane contribution, but there was a substantial decrease in the molar ellipticity of the d‐tubocurarine remaining with the membranes.