The specificity of the human uterine receptor

The aim of the present study was to assess the contribution of different parts of natural and synthetic steroid molecules in their binding to high affinity oestradiol receptor preparations obtained from whole human uteri. Fifty-five compounds were used in the study of which 38 contained the steroid nucleus. The affinity (in terms of association constants) of the compounds for the receptor was determined from competitive studies with radioactive oestradiol. As a consequence the compounds could be grouped according to their association constants for the receptor. The contribution of the individual functional groups of the steroid molecule to the binding process was analysed. The preliminary quantitative evaluation of the contribution was derived from the equation: log K=logdeltaKs + sigmalogdeltaKF where K8 is the contribution of the basic 1,3,5-(10)-oestratriene skeleton, KF the associated functional groups and K the affinity constant for the entire molecule. The main positive contribution in the binding is provided by skeleton and the 3-hydroxyl group. It is concluded that functional groups present at either the 3 or 17 position act independently of each other in the binding process. The possible synergism between the functional groups and the steroid skeleton is discussed.