Stereoselective modification of circular dichroism spectra of rat lung beta-adrenoceptor protein preparation by enantiomers of epinephrine.

The presence of beta-adrenoceptor in a rat lung membrane preparation was confirmed by stereoselective competition of enantiomers of epinephrine with labeled iodocyanopindolol. The receptor-rich protein fraction, when combined with the pharmacologically active (-)-epinephrine, exhibited specific changes in the 205-220 nm region of circular dichroism spectra, indicating that the receptor helices may be perturbed. The (+)-epinephrine combined with the lung protein produced little or no change of the spectra. Bovine serum albumin, when combined with either enantiomer of epinephrine, produced nonstereoselective alterations of the spectra. Thus, the data provide important evidence for the higher intrinsic pharmacologic activity of the natural (-)-epinephrine over the unnatural (+)-enantiomer.