Heterogeneity of endothelin receptor

The complex formed between endothelin (ET) and its binding protein was adequately stable to be separated by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) at low temperature. Cross-linking was not necessary. This simple method was applied for both qualitative (determination of molecular weight of ET binding protein) and quantitative (determination of content of ET binding protein) analyses of ET-binding protein for various organs from different mammals. Molecular weights of the major ET binding proteins were around 35 and 55 kDa in several canine organs examined. The distribution of these protein species among organs was quite different. In the case of human placenta, the predominant one showed a molecular weight of 35 kDa. We obtained several monoclonal antibodies that could immunoprecipitate ET binding activity from the solubilized human placenta membrane fraction. One of the monoclonal antibodies recognized approximately 58-kDa protein, as determined by Western blot analysis, when the gel is run in the absence of beta-mercaptoethanol.