Summary
Quantitation of fibronectin (FN) concentration is strongly influenced by FN fragmentation
with trypsin, kallikrein and plasmin. Digestion by trypsin and kallikrein leads to
a progressive decline in FN detectability by the immunoturbidimetric technique to
zero values but is associated with an increase in the height of rockets in the Laurell’s
electroimmunoassay. Plasmin mediated FN fragmentation induces a strong overestimation
of the FN content by the electroimmunoassay and, at very high enzyme concentrations,
provokes an underestimation of FN by the immunoturbidimetric technique. The decline
in FN reactivity in the immunoturbidimetric assay coincides with the disappearance
of heavy fractions migrating only slightly faster than native FN in SDS-PAGE. The
increase in the height of rockets in the electroimmunoassay is the highest when fractions
of intermediate rate of migration prevail in the SDS-PAGE pattern. Concomitant use
of these two immunoassays can distinguish native FN from its degraded form and may
possibly provide a partial explanation for discrepancies in published studies on the
concentration of circulating FN in various pathological states.
Keywords
Fibronectin - Proteolysis - Immunoassays
