Abstract. Human factor II was isolated from plasma after absorption and elution of the prothrombin complex with barium citrate and ammonium sulphate, respectively. The eluate was brought onto a QAE Sephadex A‐50 column. The fractions containing coagulation factors were pooled, concentrated and chromatographed on hydroxyapatite, after which the fractions containing factor II activity were used for the immunization of rabbits. The antiserum produced is monospecific for factor II, as could be ascertained by immunoprecipitation and by inhibition of the coagulation activity.

Abstract. Two methods are described for the preparation of human prothrombin complex on a large scale. In the first method DEAE‐cellulose DE 52 is used as an adsorbent and in the second method DEAE‐Sephadex A‐50. The results obtained with both methods are compared. The DEAE‐cellulose method is an adaptation from a previously existing small‐scale to a large‐scale preparation. The DEAE‐Sephadex method is newly developed. The amount of DEAE‐Sephadex required for adsorption, the duration of adsorption and the influence of the temperature are examined. The behaviour of Hepatitis Associated Antigen (HAA) in both methods is tested and, it is argued, that by introducing an extensive washing the risk of transmitting serum hepatitis is considerably diminished. It is concluded that the DEAE‐Sephadex method is the most suitable for a routine large‐scale production of the prothrombin complex.

The relatively low yield of factor II activity in prothrombin complex preparations gave rise to an investigation in which factor II was determined on the basis of its coagulation activity and on that of its antigenic properties during the routine preparation procedure of the complex. It appeared that factor II, measured as activity, suffered a greater loss than factor II, measured as antigen, during this procedure. This greater loss had to be attributed to changes in the conformation of the factor II protein molecule induced by the freezing step of the preparation method hitherto in use. Omission of this step led to a higher yield of factor II activity in the prothrombin complex preparation. Therefore, freezing and thawing during the preparation of the prothrombin complex should be avoided.