Additional binding sites for delta 5-androstenediol and estradiol in serum

A graphic method called close-pair-analysis is described for determining the high affinity binding parameters in a complex system. Assumptions are that the nonspecific binding is accurately measured, and that there are two specific binding classes in which the affinities (Ka) are a factor of 5 or greater apart. Using this method and equilibrium dialysis data of delta 5-Adiol and E2 binding in serum, an apparently new binding site class was found. The average Ka for both delta 5-Adiol and E2 was 8 X 10(7) L/M, with the number of binding sites ranging from 20 to 200 nM.