EVIDENCE THAT FUNCTIONAL SUBUNITS OF ANTIHEMOPHILIC-FACTOR (FACTOR-8) ARE LINKED BY NONCOVALENT BONDS

Abstract

Partially purified human antihemophilic factor (AHF, factor VIII), when treated with high concentrations of salt, dissociated into 2 components: one, of relatively low MW, possessed procoagulant activity and the other, of higher MW, formed precipitates with heterologous antiserum against AHF and supported ristocetin-induced platelet aggregation. The 2 components in the native state might be held together by noncovalent bonds. The subunits may be covalently bonded in nature but might be severed by plasma proteolytic enzymes during laboratory manipulation. Partially purified AHF was prepared from fresh human plasma in the presence of protease inhibitors, including benzamidine, soybean trypsin inhibitor, epsilon-aminocaproic acid, heparin and hirudin. Under these conditions, gel filtration in the presence of 0.25 M CaCl and 0.001 M benzamidine resulted in its separation into 2 components, having properties identical to those separated in the absence of these protease inhibitors. The inhibitor mixture blocked generation and action of streptokinase- and kaolin-activated plasmin from plasma and protected both plasma AHF and partially purified AHF from the action of thrombin. Surface-induced activation of PTA (factor XI) was partially inhibited, and that of Christmas factor (factor IX) was completely inhibited. In the native state the high- and low-MW components of preparations of antihemophilic factor are probably held together by noncovalent bonds.