Purification of Opioid Receptor in the Presence of Sodium Ion

Kil, Ho Yeong

Abstract

BACKGROUND: Purification of opioid receptor is mandatory to improve opiate analgesic medication. Recently, it was reported that sodium ion increased the number of opioid binding sites for opioid antagonist. The importance of sodium ions lead us to design appropriate affinity chromatography and binding assay for the successful purification of mu-opioid receptor to homogeneity.
METHODS
Opioid receptor was solubilized from rat brain membranes with a mixture of the detergents, CHAPS and digitonin, in the presence of protease inhibitors and 1M NaCl. The solubilized material was passed through an opioid antagonist(10cd) affinity column and a wheat germ agglutinin(WGA) column, set up in series, to obtain a partially purified receptor preparation. The partially purified receptor was further purified by repeating the affinity and lectin chromatography with smaller size column.
RESULTS
Binding of opioid antagonist [H]diprenorphine to the partially purified or purified receptors was dependent upon the presence of sodium ions. The purified receptor showed diffuse band with a medium molecular mass of 62KD upon electrophoresis. The average specific binding activity of the purified receptor was 18.8+/-2.3 pmol/mcg protein.
CONCLUSIONS
Opioid agonists and antagonists either do not bind or bind with low affinity to G protein-dissociated free opioid receptors in the absence of sodium ions. However, the free opioid receptors have a high affinity for antagonists but not agonists in the presence of sodium ions.