Stereoselective binding of β-blockers to purified rat α1-acid glycoprotein

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Abstract
The stereoselectivity of binding of four β-blockers, pindolol, propranolol, oxprenolol and acebutolol, to purified rat α1-acid glycoprotein (AAG) was examined using equilibrium dialysis. Pindolol and propranolol were bound stereoselectively to AAG, whereas binding of oxprenolol was non-stereospecific. Neither of the enantiomers of acebutolol bound to either AAG or any other plasma protein. The affinity of (+)-pindolol was 25 times that of (–)-pindolol, as determined in a single enantiomer experiment. Both enantiomers of propranolol demonstrated two classes of binding sites in AAG, the total binding for the high affinity site for (+)-propranolol being double that of (–)-propranolol, which could explain the higher binding of the (+)-enantiomer in racemate experiments. These results further showed that stereoselective binding to a rat AAG is not a property common to all β-blockers.