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

Human antihemophilic factor (AHF, factorVIII), a large plasma protein with a molecular weight of approximately two million, isdissociated by changes in ionic strength.The immunologic properties of subunitsobtained by sucrose density ultracentrifugation in 1 M NaCl and by agarose gelfiltration in 0.24 M CaCl₂ have been determined using human and rabbit anti-AHF.Asymmetric dissociation of AHF has beenidentified with formation of two subunitsin these separations: a nonfunctional highmolecular-weight (HMW) subunit similarin size to plasma AHF which is identifiedby immunoprecipitation and radioimmunoassay for AHF antigen, and an active lowmolecular-weight (LMW) subunit which isnot detected by these antigen assays. TheLMW subunit retains AHF antigens, however, for it is inactivated by both humanand rabbit anti-AHF. Antibody neutralization studies verify the presence of AHFantigens on the HMW subunit. These immunologic studies provide constraintswhich must be incorporated into models ofAHF structure.

Submitted on February 11, 1973 Revised on April 13, 1973 Accepted on May 3, 1973