Partial purification of factors XI and XIa: A comparison of their molecular size and structure

Factors XI and XIa have been purified by using affinity chromatography of plasma or contact product on heparin coupled to Sepharose. Further purification was achieved by chromatography on hydroxylapatite. Both forms of the protein co-chromatographed on Sephadex G-150 and Biogel P-300 and had identical mobility on gradient polyacrylamide electrophoresis; their molecular weight was estimated at approximately 230,000. A slight difference in electrophoretic mobility was observed when the samples were electrophoresed on polyacrylamide in 8M urea. Chemical modification studies show that both forms are inactivated by dithiothreitol and N-acetylimidazole but not by 5,5′ dithio-bis-(2-nitrobenzoic acid), iodoacetamide or EDTA.