Protein adsorption initial stage

Because of the large size of the protein and the AA required for initial adsorption, only a small region of the molecule need participate in the initial stage of the process. 

Proteins have a low diffusivity D 2 to 6 x 10 7 cm2/s. Therefore, the initial stages of adsorption are generally diffusion limited and the amount adsorbed is proportional to t1/2. If the adsorption rate, dn/dt is ... 

The rapid initial phase of salivary protein adsorption is followed by a second, comparatively slower phase of protein adsorption onto the protein-coated enamel surface. The second stage of pellicle formation is characterised by a continuous adsorption of biopolymers from saliva. This process involves protein-protein interactions between already adsorbed proteins, immobilised in the pellicle layer, and proteins as well as protein aggregates from saliva. Amino acid and Auger analyses of the pellicle layer formed on buccally carried enamel slabs [18] indicate that the adsorbed proteins reach an initial thickness in about 2-3 min, and stay at that level for about 30 min. The thickness of the pellicle then increases to about three times its initial thickness and reaches a plateau after 30-90min [5, 18, 27], Within 60min, the thickness of the in situ-formed pellicle will further increase to between 100 and lOOOnm [17, 28], dependent on the supply of locally available salivary biopolymers and the prevailing intraoral conditions [17,28,29] (fig. 2). 

The rate constants in Equation 2 include the solution concentration of the protein which is assumed to be constant in the initial stages of adsorption. Since the concentrations of plasma proteins albumin y-globulin fibrinogen are in the ratio 42.0 22.4 5.6, the rate constants from Equation 2 were weighted accordingly to give the values shown in Table II. Thus, the apparent rate constant,, ... 

However, it must be kept in mind that such a value reflects only those interactions occurring in the initial stages of adsorption at very low surface coverage. Since the glass surface is probably heterogeneous with several different types of adsorption site (see below), the initially occupied sites may not be truly representative of the surface as a whole. Also, in the intermediate and later stages of adsorption, protein-protein interactions will become important and will influence the energetics of the process. 

The irreversibility of adsorption of some proteins also emphasizes the importance of understanding the kinetics of the adsorption process. Given a situation where transport of the protein to the material surface is diffusion controlled, Eq. (2) can be used during initial stages of adsorption, where the amount of protein on the surface (A) is proportional to the product of the protein concentration in solution (C) and the square roots of protein diffusion coefficient ( )) and time (t) ... 

Since Hageman factor is thought to be helical in form, as is true with other blood proteins, it is possible that the adsorption forces between it and the surface result in an unfolding of the helix with exposure of certain active sites which in turn initiate the clotting of blood. This seems like a reasonable theory, but of course at this stage can be considered nothing more than that. 

The first stage of pellicle formation is characterised by an almost instantaneous adsorption of salivary proteins on the enamel surface. This initial adsorption process starts within seconds and probably takes a couple of minutes to be completed [13, 16-19], The thickness of this initially adsorbed layer ranges between 10 and20nm [17] (fig. 2). 

The two-stage growth process of the pellicle is of importance to the structure and function of the pellicle. The first step has been explained by an initial adsorption of discrete proteins to the enamel surface, whereas the second step is the adsorption of salivary protein aggregates in the form of micelle-like structures that move more slowly towards the interfaces, and hence give a stepwise increase in the pellicle thickness [47]. The latter structures are believed to account for the globular surface morphology of acquired salivary pellicle. 

The various stages in the interaction of a protein molecule with a surface are shown schematically in Fig. 1. Initially, protein molecules in the bulk phase approach the latex surface. Adsorption may then occur, and in some instances this is followed by... 

Most practical systems, for example, essentially all biological fluids, are multi protein systems. The various proteins compete with each other (and with other surface-active components) for adsorption at any interface present. As a rule, the interface will at first become covered by the molecules that have the highest rate of arrival (that is, the smaller ones that have the highest diffusion coefficient and the ones that occur most abundantly in the solution). At later stages, the initially adsorbed molecules may be displaced in favor of other molecules that have a higher affinity for the surface. 

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