Purification of the neurotensin receptor from bovine brain

The neurotensin receptor protein, solubilized with digitonin/asolectin from bovine cerebral cortex membranes, was purified to apparent homogeneity by affinity chromatography using immobilized neurotensin. The product exhibits saturable and specific binding of [3,11-tyrosyl-3,5-3H] neurotensin with an apparent affinity (K/sub d/ = 5.5 nM) comparable to that measured in intact membranes and crude soluble extracts. The affinity-purified material, after reduction with 100 mM dithiothreitol, in denaturing gel electrophoresis showed a single polypeptide of M/sub r/ 72,000. Under nonreducing conditions the apparent M/sub r/, however, was 50,000, suggesting the presence of intramolecular disulfide bonds. The purified neurotensin receptor was judged to be homogenous, in that (i) only a single polypeptide was detectable; and (ii) the overall purification was 30,000-50,000-fold, giving a specific neurotensin-binding activity close to the theoretical maximum