Structure-function relationships of human factor VIII complex studied by thioredoxin dependent disulfide reduction.

A highly purified, multimeric factor VIII complex composed of VIII: vWF and some factor VIII: C contained about 100 disulfides per subunit of Mr 260,000. Limited reduction of disulfide bonds in this complex by NADPH, thioredoxin reductase and thioredoxin leads to partial disaggregation of the multimeric VIII:vWF with concomitant loss of its platelet agglutinating activity in the presence of ristocetin, and with dissociation of factor VIII:C from the complex. During this event, no Mr 260,000 subunit of VIII:vWF is discernible. However, prolonged reduction results in the appearance of different multimers, and of some Mr 260,000 subunits. An N-terminal amino acid sequence for VIII:vWF was deduced. Two half-cystine residues in this sequence were shown to be involved in the reaction with thioredoxin. It appears possible that the thioredoxin system or other redox systems may play a role in regulation of factor VIII activities and of hemostatic processes in vivo.