Purification of a putative brain somatostatin receptor.

The brain somatostatin (somatotropin release-inhibiting factor; SRIF) receptor was purified by affinity chromatographic techniques. A protein of 60 kDa could be purified from rat brain. The protein was eluted from a [D-Trp8]SRIF affinity column with either sodium acetate (pH 5.5) or free [D-Trp8]SRIF. The binding of the protein to the affinity column was prevented by free [D-Trp8]SRIF or the stable SRIF analogue SMS 201-996 but not by the inactive somatostatin 28-(1-14). The purified receptor could be covalently labeled by the 125I-labeled SRIF analogue CGP 23996. Excess [D-Trp8]SRIF blocked the binding of 125I-labeled CGP 23996 to the purified receptor, but somatostatin 28-(1-14) did not affect the binding. A 60-kDa protein was also purified from the anterior pituitary cell line AtT-20, which has a high expression of SRIF receptors. In contrast, no 60-kDa protein could be purified from CHO cells, which have no detectable SRIF receptors. These findings present evidence for the purification of the SRIF receptor.