Multiple states of adsorbed proteins

The main topics to be presented include the origins of the surface activity of proteins, multiple states of adsorbed proteins, and the competitive adsorption behavior of proteins. These topics were chosen because it appears that a better understanding of each is necessary... 

Mechanismsfor MultipleStatea. Possible mechanisms that could lead to multiple states of adsorbed proteins are summarized in Table II and illustrated in Figures 1-5. 

Table II. Multiple States of Adsorbed Proteins Some Possible Mechanisms ...

Figure 1. Intrinsic heterogeneity as a cause of multiple states of adsorbed proteins, a. Occupancy effects, b. Adsorbate - adsorbate interactions.

Figure 3. Orientational effects as a cause of multiple states of adsorbed proteins.

Evidence for Multiple States of Adsorbed.Proteins. The evidence to be reviewed here supporting the existence of multiple states of adsorbed proteins derives from many types of studies (see Table III). In each study, different techniques were used to study the behavior of proteins at interfaces but none was specifically designed nor applied to investigate the possible existence of multiple states of adsorbed proteins. Furthermore, the proteins, surfaces, and objectives of each study varied. Nonetheless, this diverse data base is consistent in support of the existence of multiple states, and its diversity may therefore actually provide greater... 

The size of a molecule is an important feature because proteins form multiple contacts with the surface (e.g., 77 contact points in the case of the albumin molecule and 703 contact points in the case of the fibrinogen molecule adsorbed on silica [10]). Multipoint binding usually causes adsorption irreversibility having a dynamic nature in the absence of irreversible denaturation. The rates of desorption are, as a rule, much lower than those of adsorption, and in many cases it is virtually impossible to attain the equilibrium state desorbing the adsorbed protein [11]. In other words, the formation of one or several bonds with the surface increases the probability of adsorption of neighboring sites of the same molecule. On the other hand, the desorption of a protein molecule requires the simultaneous rupture of a large number of bonds and, for kinetic reasons, equilibrium is not attained [12-14], This corresponds to a considerable difference between the activation energies for the adsorption and desorption processes [15,16],... 

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