[Studies of progestin specific binding protein in the human prostate [I]: Studies on basic conditions for the...

Specific binding of the synthetic progestin 17 alpha-methyl-[3H]-promegestone (R5020) in the cytosol of human benign prostatic hypertrophy was studied to determine the accurate quantitative assay method. No significant effect was observed between Tris and Phosphate buffer during a buffer composition investigation. The addition of either glycerol or mercaptoethanol was effective in the enhancement of R5020 specific binding. When sodium molibdate was added into the incubation buffer, the obvious increase of 7-8S components in the SDG analysis was observed. R5020 specific binding was suppressed by the addition of CaCl2. No enhancement effect was observed by the addition of EDTA (0.1-6mM). Under the high concentration of EDTA (10-50mM), it was suppressed. SDG assay by the vertical rotor was superior to that by the swing rotor. It seemed that the long incubation time was an important factor to obtain 7-8S, which was sufficiently bounded. This estimation, however, is not assertive. Further information on the incubation time frame will be presented in the next report. It was evident that the 7-8S saturable peak alone was less than the value calculated by the charcoal assay. It was concluded that not only 7-8S but also 4S binding was included in N value by the charcoal assay. The SDG assay is recommended for the clinical receptor study, since there is not enough information concerning the character of 4S and 7-8S saturable binding in the human prostate.