In search of early pregnancy factor: characterisation of active polypeptides isolated from pregnant ewes' sera.

Further biochemical characterisations of the 20 kd and 67 kd EPF active polypeptides from pregnant ewes' sera are described. Both polypeptides are shown to possess compact, disulphide linked domains which are almost totally resistant to proteolytic attack without prior reduction. In contrast to previous reports on the influence of ammonium sulphate on the expression of EPF activity, neither the biochemical nor the activity characteristics of either polypeptide is changed by ammonium sulphate fractionation. In addition, direct comparative studies have been performed which clearly distinguish the EPF active polypeptides from the known ovine hormones, prolactin, placental lactogen and growth hormone.