The heterogeneous exchange process whereby IgG molecules adsorbed on a
hydrophilic silica surface are replaced by fibrinogen molecules from
the solution has been investigated by means of I-125 radiolabeling. Tw
o characteristic times appear both in the desorption and replacement p
rocesses. At short times (on the order of 1 h), the process seems to c
orrespond to an exchange mechanism which can be modeled by a first-ord
er kinetic reaction with respect to the fibrinogen molecules. Furtherm
ore, it also appears to be of first-order with respect to the adsorbed
IgG molecules. The exchange rate constant is equal to (3.84 +/- 0.05)
x 10(5) L mol(-1) h(-1). This generalizes previous conclusions drawn
from homogeneous exchange studies both on polymer and protein systems.
The long term behavior of the replacement process is characterized by
a time scale which is identical to that of the desorption process. It
thus seems to correspond to a desorption/readsorption process.