Radioimmunoassay of human fibrinopeptide B and kinetics of fibrinopeptide cleavage by different enzymes.

A B S T R A C T Thrombin converts fibrinogen to fibrin monomer by cleaving fibrinopeptides A and B (FPA and FPB) from the amino terminal ends of the A(a) and B (P) chains. A radioimmunoassay capable of mea- suring the A peptide in human blood as an index of thrombin action in vivo has been described previously. This paper describes the development of a radioim- munoassay for FPB and the use of both assays in the demonstration of distinctive patterns of cleavage of the amino terminal ends of the A(a) and B(P) chains of fibrinogen by various enzymes.