Evidence for the participation of both activated factor XII and activated factor IX in cold-promoted activation of factor VII

Abstract The activation of 125 I-Factor XII and of 125 I-Factor IX in plasma during the cold-promoted activation of Factor VII was studied. Limited proteolysis of Factors XII and IX, a measure of activation, was determined from radioactivity profiles of reduced polyacrylamide gels following electrophoresis in the presence of sodium dodecyl sulfate. Significantly greater formation of Factor IX a and Factor XII a was found in citrated plasma incubated at 4° from four subjects whose Factor VII activity increased compared to plasma from five subjects whose Factor VII activity did not increase. Addition of an anti-Factor IX antiserum to citrated plasma inhibited 50% of the observed cold-promoted activation of Factor VII. The data are consistent with the hypothesis that both Factor XII a and Factor IX a are direct activators of Factor VII during cold-promoted activation of Factor VII in citrated plasma.