A fibrinogen fragment D (D intermediate) with calcium binding but without anticlotting properties

Abstract

Plasmin digestion of fibrinogen in the presence of Ca 2+ or of EGTA leads to the formation of two sets of fragments, designated Dcate and D EGTA, respectively. Fragments Dcate, in contrast to D EGTA, bind one calcium ion and are anticlotting. Both these properties of Dcate are related to a 13-kDa carboxyl-terminal stretch of its γ-chain, which is missing in D EGTA. The molecular weights of the γ-chains of Dcate and D EGTA are 38000 and 25000 respectively. Now we have prepared a D-fragment, Dint, which has a γ-chain with a molecular weight of 29000. Dint binds one calcium ion per molecule but has no anticlotting properties. Thus the Ca 2+-binding site of Dint (and Dcate) is directly dependent on the 4-kDa piece of the γ-chain that is present in Dint but not in D EGTA. As a consequence, the anticlotting properties of Dcate reside in the γ 9-kDa stretch that is absent in Dint.