Photoaffinity labelling of gonadotropin releasing hormone binding sites in human epithelial ovarian carcinomata

A photoaffinity labelled derivative of D-Lys6]-GnRH was prepared with a bifunctional photolabile reagent (4-azidobenzoyl)-N-hydroxysuccinimide. In rat pituitary membranes, this analog retained high binding affinity (Ka = 0.12 x 10(9) M-1) consistent with a single class of receptors. The analog was iodinated and used for the identification of GnRH binding sites in human epithelial ovarian carcinomata. By sodium dodecyl sulfate electrophoresis in 10% polyacrylamide gel the presence of two labelled components could be demonstrated: a high molecular weight component of 63,200 and a smaller component of 46,000. Competition experiments with unlabelled ligand suggest that it is the high molecular weight component which specifically binds GnRH.