Immunologic Studies of Antihemophilic Factor (AHF, Factor VIII). V. Immunologic Properties of AHF Subunits Produced by Salt Dissociation

Human antihemophilic factor (AHF, factor VIII), a large plasma protein with a molecular weight of approximately two million, is dissociated by changes in ionic strength. The immunologic properties of subunits obtained by sucrose density ultracentrifugation in 1 M NaCl and by agarose gel filtration in 0.24 M CaCl₂ have been determined using human and rabbit anti-AHF. Asymmetric dissociation of AHF has been identified with formation of two subunits in these separations: a nonfunctional highmolecular-weight (HMW) subunit similar in size to plasma AHF which is identified by immunoprecipitation and radioimmunoassay for AHF antigen, and an active lowmolecular-weight (LMW) subunit which is not detected by these antigen assays. The LMW subunit retains AHF antigens, however, for it is inactivated by both human and rabbit anti-AHF. Antibody neutralization studies verify the presence of AHF antigens on the HMW subunit. These immunologic studies provide constraints which must be incorporated into models of AHF structure.