Testicular GnRH receptors: photoaffinity labeling and fluorescence distribution studies

Specific GnRH receptor proteins of purified rat Leydig cells and membrane preparations were identified using an 125I-labeled bioactive photoaffinity derivative of GnRH. Sodium dodecyl sulfate polyacrylamide gel electrophoresis resulted in the identification of two specific components with apparent molecular weights of 60,000 and 54,000 daltons. Fluorescent visualization of GnRH receptors in these cells, utilizing a bioactive rhodamine derivative of the hormone, indicated that the fluorescently labeled receptors were initially distributed uniformly on the cell surface and then formed clusters which subsequently internalized (at 37 degrees C) into endocytic vesicles. These processes were dependent on specific binding sites for the rhodamine-labeled peptide on Leydig cells. These findings indicate further characterization of the testicular GnRH receptors and may have important implications towards the understanding of the molecular events involved in the action of the hormone in the testis.