Human fl - adrenergic receptors Simultaneous purification of 1 ) i - and fl 2 - adrenergic - receptor peptides

,6-Adrenergic receptors from basal membranes of human placenta were purified from digitonin extracts by sequential rounds of affinity chromatography, hydrophobic chromatography, ion-exchange chromatography and steric-exclusion h.p.l.c. Basal membranes display both j%and fl2-adrenergic receptors, in the ratio 65:35. Affinity chromatography, hydrophobic chromatography on heptylamine-Sepharose and ionexchange chromatography on DEAE-Sephacel removed most of the contaminating pro.teins, and final purification of the receptor to apparent homogeneity was achieved by steric-exclusion h.p.l.c. The purified receptors showed Mr 67000 on SDS/polyacrylamide-gel electrophoresis under reducing conditions. Specific binding of radioligand to the purified ,-adrenergic receptors displayed stereoselectivity, and the agonist competition profiles demonstrated the presence of both ,1and fl2-receptors. By using the subtype-selective ligands CGP-20712A (fl,-selective) and ICI118,551 (/12-selective), the purified Mr-67 000 species was shown to be composed of equivalent amounts of 81and /J2-adrenergic receptors. Affinity chromatography on Sepharose-alprenolol and sequential elution with 1 /uM-CGP-20712A followed by 100 ,UM-(-)-alprenolol permitted /1-adrenergic receptors to be resolved from the mixture of 8,-/fl2-adrenergic receptors. The pharmacologically distinct human ,81and fl2-adrenergic receptors are shown to be structurally very similar peptides.