Summary
In anticipation of a future clinical application of plasma fibrinopeptide B (FPB)
measurement, we studied the stability of FPB in an ultrafiltrate of normal plasma,
normal urine and alkaline buffer by measuring the immunoreactivity of the peptide
by FPB radioimmunoassay using anti FPB serum (R-29). FPB was unstable in an ultrafiltrate
of plasma and urine and demonstrated a temperature dependent loss of activity. In
plasma ultrafiltrate the loss of immunoreactivity was not significant during the first
24 hours, however, 92% of the peptide activity was lost at the end of seven days at
25° C and 37° C. The rate of FPB degradation in urine was comparable. The peptide
was stable in an alkaline buffer (pH 8.5) at temperatures ranging from �10° C to 37°
C or in plasma ultrafiltrate or urine when incubated at �10° C. Treatment with carboxypeptidase
B or leucine aminopep- tidase for two hours at 37° C (enzyme/substrate molar ratio
of up to 1:100) did not cause a loss of FPB immunoreactivity. EDTA (1.0 mM) and Trasylol
(500 units/ml) completely stabilized the peptide in a plasma ultrafiltrate.
