CALCIUM MODULATES PLASMIN CLEAVAGE OF THE FIBRINOGEN-D FRAGMENT GAMMA-CHAIN N-TERMINUS - MAPPING OF MONOCLONAL-ANTIBODY J88B TO A PLASMIN SENSITIVE DOMAIN OF THE GAMMA-CHAIN

Plasmin sensitive sites are found on the A alpha, B beta and gamma cha ins of fibrinogen at regions joining the two C-terminal D fragments wi th the central E fragment. We have developed a monoclonal antibody (Mo Ab) reactive with this plasmin sensitive region on the human fibrinoge n gamma chain and mapped its epitope. MoAb J88B reacts with gamma chai ns of both native as well as with reduced and denatured fibrinogen and fibrin, the CNBr fragment of the fibrinogen central domain, plasmin c leaved fragments D, gamma-gamma dimers, but not with plasmic fragments E. These data indicate that J88B maps to the plasmin sensitive domain localized to gamma(63-78). MoAb J88B failed to react with synthetic p eptide gamma(70-78), which suggests that the epitope includes the newl y exposed N-terminal residues gamma(63-70) Of the early plasmic fragme nt D1A. As calcium has a marked influence on plasmin cleavage of C-ter minal sites on the gamma chain, the effects of calcium on modulating p lasmin cleavage of D1A to D1 were assessed in the absence or presence of J88B. The results indicated that calcium delays and J88B (+/- calci um) protects the gamma chain from plasmin cleavage at the N-terminus o f D1A, suggesting that this enzymatically labile site is calcium-sensi tive. Thus, MoAb J88B should prove useful in studies examining the str ucture of plasmin cleaved fibrinogen and fibrin.