Autoactivation of human blood coagulation factor XII on dextran derivatives of different molecular weight

We prepared a derivative of dextran T40 (average M(r) 43,000) from which fractions of different M(r) but with equal charge density were obtained and tested for their ability to promote autoactivation of human blood coagulation factor XII. The mechanism of autoactivation appeared dependent upon the M(r) of the polymer used. Thus, with polymers of 38,000 M(r) or higher only alpha-factor XIIa was formed and the reaction could be completely described in terms of a simple second-order mechanism of autoactivation. With smaller polymer molecules beta-factor XIIa became a major reaction product and as a result of this the autoactivation kinetics did not adhere to the second-order mechanisms thus far described.