A molecular weight study of the rat brain delta opioid receptor

The molecular weight of the rat brain delta opioid receptor, studied with antiidiotypic antibodies to anti-leucine enkephalin that mimic leucine enkephalin in binding to the receptor, was examined by molecular sieving and Western Blots under nondenaturing, denaturing and reducing conditions. The receptor appeared to be 55-65 kDa, which on solubilization may exist in equilibrium with receptor oligomers of 130-150 kDa and aggregates of > 200 kDa. These forms may also represent aggregation due to solubilization. A 38-43 kDa molecule was considered a minor form of the receptor in the brain.