ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY IDENTIFICATION OF FIBRINOGEN BANKS PENINSULA (GAMMA-280TYR-]CYS) - A NEW VARIANT WITH DEFECTIVE POLYMERIZATION

Fibrinogen Banks Peninsula was identified in the mother of a patient r eferred for investigation following recurrent epistaxis. Coagulation t ests revealed prolonged thrombin and reptilase times and a decreased f unctional fibrinogen level, Thrombin-catalysed release of fibrinopepti des A and B was normal. and no abnormalities were detected by DNA sequ encing of the regions encoding the thrombin cleavage sites in the A al pha and B beta genes, Reducing SDS-PAGE and reverse-phase HPLC analysi s of purified fibrinogen chains were normal, as was electrospray ioniz ation mass spectrometry (ESI-MS) analysis of isolated A alpha and B be ta chains. However ESI-MS revealed a mass of 48 345 D for the isolated gamma chains, 31 D less than the measured mass of control chains (45 376 D). Since normal and abnormal gamma chains were not resolved, this implies a 60-62 D mass decrease in 50% of the molecules. A 60 D decre ase was confirmed when DNA sequencing indicated heterozygosity for a m utation of Tyr-->Cys at codon 280 of the gamma chain gene. Fibrin mono mer polymerization revealed a delayed lag phase and reduced final turb idity and although factor XIIIa crosslinking of fibrinogen was normal. it is likely that this delay is due to impaired D:D self association. Recent crystallographic studies show residues gamma 280 and gamma 275 make contact across the D:D interface, suggesting a similar mechanism for the polymerization defects in fibrinogens Banks Peninsula and Tok yo II (gamma 275Arg-->Cys).