HUMAN FACTOR-VIII - A CALCIUM-LINKED PROTEIN COMPLEX

  • 1 January 1983
    • journal article
    • research article
    • Vol. 62  (5) , 1006-1015
Abstract
The possible role of Ca2+ as an essential constituent part of the human factor VIII complex was investigated by stability studies, metal determinations and gel filtration experiments. In citrated plasma, the factor VIII coagulant activity (VIII:C) deteriorated during storage in a biphasic manner. Collection of blood in heparin, instead of chelating anticoagulants, or neutralization of citrate by addition of CaCl2 to heparinized citrate phosphate dextrose (CPD) plasma rendered VIII:C noticeably stable. At physiologic levels of ionized Ca, VIII:C was almost completely stable during incubation of plasma for 6 h at 37.degree. C. The influence of other divalent ions was also studied. Highly purified factor VIII complex was subjected to atomic absorption spectrophotometric analysis and found to contain about 1.0 mole Ca/220,000 daltons. This intrinsic Ca could be readily removed by EDTA. When heparin plasma and CPD plasma were chromatographed on Sepharose CL-6B at 37.degree. C, all the factor-VIII-related activities eluted together as large protein complexes. In contrast, factor VIII coagulant antigen (VIII:CAg) and factor-VIII-related antigen (VIIIR:Ag) were completely dissociated upon exposure to EDTA. Human factor VIII circulates in normal plasma as a Ca-linked protein complex.