Identification and partial purification of a hydrophobic protein component associated with [3H]spiroperidol-binding...

The binding activity of radiolabelled neuroleptic drugs has been used to biochemically and pharmacologically characterize the dopamine receptor in brain. An extract which binds [3H]spiroperidol and exhibits stereoselectivity for (+)- and (-)-butaclamol, has been isolated from the calf striatal microsomal fraction. Specific binding activity in the chloroform-methanol extract of this preparation is enhanced over that of the crude homogenate. The highest specific binding of the chloroform methanol extract is associated with the crude phospholipid component which is enriched in hydrophobic proteins and acidic phospholipids. Subfractionation of the crude phospholipid extract by gel filtration (Sephadex LH-20) yields multiple peaks of [3H]spiroperidol binding activity, however four major zones of specific binding activity were detected. These results demonstrating a close association of phospholipids with a dopamine binding site suggest a functional role for proteolipid in receptor recognition and regulation.