Search

The adsorption of fibrinogen to a hydrophilic quartz surface was studied by transmission electron microscopy using a negative staining technique to visualize the protein. The distribution of adsorbed fibrinogen was random at low surface concentrations and low bulk concentrations (0.29 nM) when analyzed as the pair correlation function g(r). At higher concentration (0.73 nM) an end-to-end polymer polycrystalline structure was seen at the surface, indicating attractive interaction between the ends of the rod-shaped molecule. The polycrystalline pattern was broken up at higher concentrations and snowflake-like crystals were formed. The results indicate the presence of weak attractive forces between the ends of fibrinogen molecules. [ABSTRACT FROM AUTHOR]

Adsorption of ferritin to a hydrophobic solid surface was studied by transmission electron microscopy. At low bulk concentrations adsorption is initiated at a few sites and continues by growth of clusters at these sites. The nucleation-and-growth-like kinetics gives an acceleration of the apparent binding rate which is damped by mass transport limitation. The clusters grow to a critical size and dissociate rapidly from the surface. This process of accelerated binding and critical dissociation can be seen repeatedly during adsorption of the protein. At high bulk concentrations, the surface is covered with protein during the first seconds of incubation, but the adsorbed layer then becomes unstable and dissociation is seen within the first minute of incubation, resulting in a clustered spatial distribution of adosrbed protein. These findings suggest that protein adsorption reaches an equilibrium, but that the kinetics of the process is discontinuous. [ABSTRACT FROM AUTHOR]

The binding of monoclonal antibodies to surface-adsorbed antigen was measured by ellipsometry. Mouse IgG-antibodies directed against dinitrophenyl were used. The different binding affinities to free hapten in solution had previously been determined. — The experimental findings indicate that the mechanism of heterogeneous antibody-antigen reactions is more complex than the corresponding reaction mechanism in solution. The initial binding of antibodies easily becomes diffusion-rate-limited. The progressive, forward-reaction rate is continuously retarded. The reverse reaction is slow enough to make the total reaction practically irreversible. Experimental data were considered, especially in order to analyze the decreasing forward reaction rate. — It was found that the forward rate constant has a dependence on time, such that k(t) ∝ k1t−h, where 0

The kinetics of adsorption and the spatial distribution of adsorbed ferritin was studied by transmission electron microscopy (TEM) using a hydrophobic quartz grid as solid substrate. It was found that the initial adsorption process appears as a growth of molecular clusters at the liquid-solid interface. The rate of adsorption was limited by the mass transport of ferritin from the bulk to the liquid-solid interface. — Density-density correlation analysis c(r) of the mass distribution of protein within the clusters by computer-aided image analysis showed a fractal dimension df=1.05 at short distances (100 nm). The fractal dimension of the clusters is smaller than values obtained from theoretical models of two-dimensional diffusion-limited aggregation, indicating that the mass transport limitation of the adsorption process does not determine the structure of ferritin clusters. More complex models have to be used to account for the experimental observations. [ABSTRACT FROM AUTHOR]

Some theoretical models describing the adsorption of proteins from solution are investiated. Computer simulations are carried out on a hexagonal lattice that allows lateral interactions between adsorbed protein molecules to be incorporated in the model. Diffusion limited adsorption determines the amount of particles at the surface and aggregation is allowed by lateral diffusion along the surface. The computer model can be characterized as a two-dimensional, stochastic, cellular automation where the surface sites are arranged on a hexagonal lattice. The fate of every lattice site, or cell, is updated in discrete time steps. Different rules concerning nearestneighbor interactions were tested, giving both irreversible and reversible diffusion-limited aggregation (DLA). — The fractal dimensions of individual clusters were extracted from simulated aggregates and found to be consistent with literature values on irreversible and reversible DLA in two dimensions. By comparing computer simulated aggregation to experimental electron micrographs of adsorbed ferritin layers some conclusions can be drawn concerning the adsorption of ferritin to hydrophobic quartz surfaces. The adsorbed protein molecules must, most probably, the mobile along the surface with a diffusion constant considerably lower (5 · 104) than in the bulk solution. The initial aggregation could be well described by reversible DLA-clustering (at θ=0.015), but at higher surface coverages of proteins (at θ=0.1) the present model could not account for the low experimentally observed fractal dimension (df=1.05). [ABSTRACT FROM AUTHOR]