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

A four-step procedure is described for the isolation of the polypeptides which are responsible for a major portion of the EPF activity present in pregnant ewes' sera between 3-8 weeks gestation. The procedure utilises large-scale molecular size fractionation on hollow fibres in combination with conventional ion-exchange chromatography and HPLC gel permeation. It yields two homogeneous active fractions. One contains a single polypeptide of molecular weight approximately 20K, the other a 67K polypeptide. When compared on either a weight or molar basis the 20K polypeptide was at least an order of magnitude more active in the rosette inhibition test than the 67K polypeptide. The 20K polypeptide appears to represent the major form of RIT active material (EPF) present in pregnancy sera at this stage of gestation in the ewe.