Kinetic data of cytoplasmic estradiol receptor.

Association and dissociation equilibrium constants and rate constants have been determined in human breast cancer tissues, human lymph node metastases, experimentally induced rat mammary tumors and pooled uteri of normal rats. When the dissociation constants gained from the Scatchard plot applying the Chamness correction were compared to those calculated as the quotient of the rate constants, relatively large differences were found, predominantly due to the values of measured association rate constants. In contrast, there were no specific differences between the constants of distinct tissues. The differences among the association rate constants were presumably caused by a contamination of cytosols by steroid binding proteins of serum. Increasing amounts of serum added to tissue samples resulted in an increasing interference with the determination of the dissociation constants using the Scatchard analysis.