Binding of estradiol receptor complexes to isolated human breast chromatin

Summary The interaction of estradiol-receptor complexes and isolated human breast tumor chromatin was studied under equilibrium conditions.The estradiol-receptor complexes bound specifically to the chromatin of hormone dependent tumors and showed a single class of binding sites with a Ka of 0.96 × 10¹⁰m^–1 and a binding capacity of 1.5 pmoles/mg DNA. The binding was a temperature-dependent process and involved a transformation of the receptor protein.The heat-activated hormone-receptor com-plex was more active than the 8S form in the binding phenomenon. The specific interaction of estradiol-receptor complex with isolated chromatin was saturable and sensitive to conditions of temperature and ionic strength. Furthermore under optimal conditions no acceptor sites were detected in chromatin of hormone independent tumors.Dedicated to ProfessorLuis F. Leloir on the occasion of his 70th birthday.