Immunochemical studies of human factor XIII.
Plasma factor XIII circulates as a noncovalently associated, tetrameric zymogen (a2b2). The b subunit may act as a carrier protein for the a subunit, which possesses the potential catalytic function. In order to define interactions that occur between the two subunits, a sensitive and specific RIA for the b subunit has been developed. Purified plasma factor XIII was incubated with thrombin and chromatographed on organomercurial agarose to separate the subunits. Pure b chain eluted in buffer containing CaCl2. This material was used as the standard b preparation, both for preparing a monospecific antiserum and for establishing the assay. The linear range of the assay is 7 to 700 ng/ml (Ca. 0.1 to 10 nM b subunit), with a minimum detectable dose of l. Data were analyzed by use of the logit-log transformation of antigen-binding curves. The dose-response slope for standard b is -2.76 + or - 0.20, with a potency (ED50) of 74.9 + or - 6.5 ng/ml. This RIA is also valid for determining b subunit concentration of plasma and serum. The dose-response slope for the plasma system is -2.69 + or - 0.20 with an ED50 identical to that of the purified system. By this method the mean b subunit concentration in normal human plasma (corrected for anticoagulant) is 13.8 micro g/ml (ca. 0.15 micro M). The concentration in serum is 13.6 micro g/ml, which shows that b subunit is quantitatively recovered after coagulation has occurred.
D000818:Animals; D000915:Antibody Affinity; D001665:Binding Sites; D002352:Carrier Proteins / Q000276:immunology*; D004306:Dose-Response Relationship, Immunologic; D004792:Enzyme Precursors / Q000276:immunology*; D005176:Factor XIII / Q000276:immunology*; D005260:Female; D006801:Humans; D008297:Male; D011817:Rabbits; D011863:Radioimmunoassay
D002352:Carrier Proteins; D004792:Enzyme Precursors; D005176:Factor XIII