Kinetics of exchange processes in the adsorption of proteins on solid surfaces.

Abstract

The homogeneous exchange process whereby IgG molecules adsorbed onto latex particles are replaced by IgG molecules from the bulk solution was studied by means of ts radiolabeling. The exchange mechanism was Investigated on surfaces saturated with either labeled or unlabeled proteins in the presence of a solution of the opposite species in two sets of independent experiments. After rinsing of the surface by pure buffer followed by supplementary IgG adsorption, the exchange process.followed a kinetic law of first order with respect to the IgG molecules from the bulk solution, and the apparent exchange rate constant was (2.3 ± 0.4) x 10-5 cm hr'1.One of the main differences between adsorption processes of "small" molecules and of macromolecules on solid surfaces is that macromolecules can reach the surface by two different mechanisms (1): by direct adsorption or by a progressive exchange reaction. In the first case the molecules reach the adsorption surface directly on free available space. In contrast, for the exchange mechanism the molecules reach the surface by progressive removal of already-adsorbed macromolecules. This occurs in particular when the surface is saturated with preadsorbed molecules. This second process has never been observed in the adsorption of small molecules on surfaces.The physical origin of this second adsorption process lies in the fact that macromolecules interact with a surface through several links. These links along the macromolecule change with time, even if the molecule is in an equilibrium configuration. Interactions between macromolecule and surface must thus be considered as a dynamic and not a static process. Moreover, macromolecules are not rigid bodies. Thus, if such a molecule enters into the vicinity of a surface already covered by adsorbed macromolecules, it can change its conformation and diffuse into the adsorbed layer. Once part of the backbone of the diffusing molecule reaches the adsorption surface, it interacts with it. This interaction can then be followed by sequential, segmental, reptation-like adsorption of the molecule, in competition with the dynamic process of the formation and annihilation of links of previously adsorbed macromolecules. Finally, the diffusing molecules progressively replace those already adsorbed on the surface, completing the exchange process.Such processes have been observed for synthetic polymers (2) as well as for proteins (3,4) by means of radioactive labeling techniques. NevertHeless, and in spite of a great number of investigations, little is known about adsorption processes of macromolecules (5). Let us rapidly summarize the main results that have been established. (i) The affinity of proteins for a given surface usually increases with their molecular weight. High molecular weight proteins usually exchange preferentially with lower molecular weight adsorbed proteins (6, 7). (ii) The higher the hydrophobicity of the surface is, the larger is the adsorbed quantity (8, 9). (iii) These amounts are maximal for pH values close to the ...

Solid supports for microarray immunoassays

“…Close proximity between the adsorptive surface and the protein's reactive site could influence the affinity for a ligand unfavourably. Surfaces may also be susceptible to exchanging adsorbed protein with proteins in the surrounding solution (Ball et al, 1994;Lutanie et al, 1992). Stringent washing can destabilize protein attachment.…”

Protein adsorption on solid surfaces

“…A dynamic protein exchange is typically observed when two or more proteins are allowed to adsorb simultaneously to a surface. The exchange also occurs between proteins at the interface and proteins in solution [54,55]. For plasma proteins, the exchange process, which is usually governed by mass transport and the respective affinity of a given protein for the surface, is often referred to as the 'Vroman' effect.…”

Fibronectin facilitates adhesion of K562 leukemic cells normally growing in suspension to cationic surfaces

“…It should be recalled that a layer of adsorbed protein does not undergo exchange when exposed to the same protein, but does so if a solution containing a different protein is added. [28][29][30] Thus, it may be hypothesized that when the growth medium containing both the cells and serum proteins is added to flasks covered with BSA, the adsorbed BSA proteins undergo exchange with the other FBS serum proteins. Consequently, BSA proteins are displaced and the FBS proteins adsorb to polylysine.…”