BINDING OF [TAMOXIFEN-H-3] IN RAT UTERINE CYTOSOLS - COMPARISON OF SWINGING BUCKET AND VERTICAL TUBE ROTOR SUCROSE DENSITY GRADIENT ANALYSIS

The interaction of the anti-estrogen tamoxifen with rat uterine estrogen receptor was studied using swinging bucket and vertical tube rotor techniques of sucrose density gradient analysis. Tamoxifen inhibits binding of 3H-estradiol to the 8S estrogen receptor protein, whereas the swinging bucket rotor technique of sucrose density gradient analysis 3H-tamoxifen appears to bind to an estradiol specific protein which sediments at 4-5S. Using rapid sucrose density gradient analysis with a vertical tube rotor 3H-tamoxifen showed estrogen specific binding in the 8S region. Conventional techniques of sucrose density gradient analysis apparently are unsuited for investigation of low affinity ligand interactions with estrogen receptor proteins, since rapid dissociation of complexes can result in ligand binding to nonreceptor proteins.