Fig. 4
[32P]FKBP12 binding to sperm. Caput and cauda sperm were isolated from the epididymis, washed, and incubated with [32P]FKBP12 in PBS containing 1 mM DTT, 1 mM EGTA, and 2 mg/ml BSA for 1 hr at 4°C. The sperm were then pelleted, washed two times with ice-cold incubation buffer, and counted. Specific binding was determined by subtracting [32P]FKBP12 binding in the presence of 1 µM FK506 from total [32P]FKBP12 bound. All binding experiments were done in duplicate and repeated three times. Error bars are standard deviations of the mean. [32P]FKBP12 bound specifically to caput sperm but not to cauda sperm.