[Studies on a radioligand-receptor binding assay of human chorionic gonadotropin in rat testis]

A radioligand-receptor binding assay for human chorionic gonadotropin (HCG) has been established with cell membranes preparation of rat testis. Partially purified cell membranes preparation was prepared from rat testis by sucrose density gradient ultracentrifuge. The binding assay was performed by incubating 125I-HCG with rat testis cell membranes preparation at 30 degrees C for 1.5 h in a total incubation volume of 0.5 ml. Scatchard plot analysis for the binding assay revealed a linear binding plot and yielded a bound capacity of testis cell membranes receptors of 0.36 x 10(-12) mol/micrograms protein. KD of 0.45 x 10(-10) mol/L. Hill coefficient was 0.976. Studies on the kinetics of the reaction of radioligand-receptor binding showed that the mean values for the association rate (k1) and dissociation constants (k2) were individually 0.41 x 10(-3) pmol/min and 2.12 x 10(-3) pmol/min; the dissociation plot was two-phase, with 15 x 10(-3) pmol/min of fast-phase and 1.5 x 10(-3) pmol/min of slow-phase.