Purification of rat brain, rabbit aorta, and human platelet thromboxane A2/prostaglandin H2 receptors by immunoaffinity chromatography employing anti-peptide and anti-receptor antibodies.

In the present study, a new polyclonal antibody (TxAb) was raised against native thromboxane A2 (TXA2)/prostaglandin H2 (PGH2) receptor protein. Previously developed anti-peptide antibodies (P1Ab, P2Ab) and TxAb were then used to prepare immunoaffinity columns to purify TXA2/PGH2 receptors from platelets, brain, and aorta. In platelets, SDS-polyacrylamide gel electrophoresis revealed the purification of a 55-kDa protein by each affinity column. Identification of this protein as the TXA2/PGH2 receptor was based on: 1) an identical electrophoretic mobility to authentic receptor; 2) immunoblotting of TxAb against P1Ab and P2Ab-purified protein; 3) immunoblotting of P1Ab/P2Ab against TxAb-purified protein; and 4) specific [3H]SQ29,548 binding to TxAb-purified protein. P1Ab/TxAb purification of receptors from brain revealed a major protein band at 55 kDa. Furthermore, the eluates from ligand affinity chromatography confirmed the presence of this 55-kDa protein in brain (which was immunoblotted with TxAb), and contained specific [3H]SQ29,548 binding. In addition to the 55-kDa protein, P1Ab/TxAb also purified a minor protein in brain at 52 kDa, which when concentrated, cross-blotted with TxAb and P1Ab. This finding indicates sequence homology between the 55- and 52-kDa proteins. Independent identification of brain TXA2/PGH2 receptors was provided by P2Ab/TxAb immunohistochemistry, which demonstrated specific labeling of discrete myelin-containing fiber tracts. P2Ab/TxAb purification of TXA2/PGH2 receptors from aorta also revealed a major protein band at 55 kDa and a minor band at 52 kDa. These results represent the first purification of TXA2/PGH2 receptors from either brain or aorta.