they sediment at 7-8s on sucrose density gradients , they bind ligands with high affinity ( kd approximately 4 nm for r5020 ; kd approximately 2 nm for progesterone ) , they bind only progestins specifically , and they are thermolabile ( t1/2 at 37 c is approximately 15 min ) .
C0033308
progesterone
C0033306
progestins