Protein Layers

The reactions of biopolymers at interfaces fonn tire basis of some extremely important industrial processes. The primary process in all cases is tire adsorjDtion of biomolecules, usually proteins. If ultimately living cells are adsorbed, tliis always takes place onto a preadsorbed protein layer (which may be secreted by tire cells themselves [130]). These processes can be classified into tliree categories ... 

Further improvements can be achieved by replacing the oxygen with a non-physiological (synthetic) electron acceptor, which is able to shuttle electrons from the flavin redox center of the enzyme to the surface of the working electrode. Glucose oxidase (and other oxidoreductase enzymes) do not directly transfer electrons to conventional electrodes because their redox center is surroimded by a thick protein layer. This insulating shell introduces a spatial separation of the electron donor-acceptor pair, and hence an intrinsic barrier to direct electron transfer, in accordance with the distance dependence of the electron transfer rate (11) ... 

The other method of monolayer transfer from the air/water interface onto solid substrates is illustrated in Figure 2. This method is called the Langmuir-Schaefer technique, or horizontal lift. It was developed in 1938 by I. Langmuir and V. Schaefer for deposition of protein layers. Prepared substrate horizontally touches the monolayer, and the layer transfers itself onto the substrate surface. The method is often used for the deposition of rigid monolayers and for protein monolayers, hi both cases the apphcation of the Lang-muir-Blodgett method produces defective films. 

The Langmuir-Blodgett (LB) technique was successfully applied for the deposition of thin protein layers (Langmuir and Schaefer 1938, Tiede 1985, Lvov et al. 1991). LB organization of protein molecules in film not only preserved the structure and functionality of the molecules, but also resulted in the appearance of new, useful properties, such as enhanced thermal stability (Nicolini et al. 1993 Erokhin et al. 1995). 

The LB technique was chosen for covering the spheres because it was shown to provide enhanced thermal stability of many types of proteins in deposited layers (Nicolini et al. 1993, Erokhin et al. 1995, Antolini et al. 1995), which no other technique is able to achieve. Since only the upper protein layer is involved in the catalytic activity, no special attention was paid to check whether the deposited layer is a monolayer or multilayer. However, the samples were thoroughly washed to remove protein molecnles not bound covalently to the sphere surface, since during the functional test these molecules could contribute to the measured apparent catalytic activity. 

Two-dimensional protein layer orientation could be also effected by metal-ion coordination Monolayer of iminodiacetate-Cu(II) lipid was successfully employed as substrate for oriented immobilization of proteins naturally displaying histidine residues on their surface [37]. Affmity-resin-displaying Ni(II) complexes could also be successfully employed for oriented protein immobilization [38]. 

M Shelled creatures such as mussels and snails are Marble is readily workable remarkable constructors of casings of Ca carbonate and has challenged artists with protein layers. throughout the ages. 

Figure 4c shows one example of the time course of an SPR angle shift during exposure of a NH2-SAM to culture medium supplemented with 2% fetal bovine serum (FBS). It also includes the time course of the fraction of adherent cells on the same surface determined by TIRFM observation (Fig. 2). The SPR angle shift rapidly increased, and then leveled off within a few minutes. Cells adhered much more slowly than proteins. Those results indicated that serum proteins in a medium rapidly adsorbed to the surface then, cells interacted with the adsorbed protein layer, as shown schematically in Fig. 5.

When the surfaces of the protein molecules and the sorbent are predominantly polar, it is probable that some hydration water is retained between the adsorbed protein layer and the sorbent surface. Then, the contribution from changes in the state of hydration to the Gibbs energy of protein adsorption, AadsGhydr, will be minor. When the surfaces are... 

The 3D structure of a native protein (in aqueous solution) is only marginally thermodynamically stable and it is sensitive to changes in its environment. It is, therefore, not surprising that adsorption is often accompanied by rearrangements in the protein s 3D structure. It is commonly observed experimentally that the thickness of an adsorbed protein layer is comparable to the dimensions of the protein molecule in solution. It indicates that the adsorbed protein molecules remain compactly structured. 

Thickness of Adsorbed Protein Layers on Glass Adsorption of Proteins in Multilayers... 

It is important, however, to remove the protein layer from the surface over which the air/liquid meniscus is displaced during the measurement so as to assure that the conditions of flow with and without the layer in the capillary are totally comparable. Using this method we find that in the case of bovine serum albumin very thick layers are formed layers whose thickness grows in direct proportionality to albumin concentration up to 15% w/v, at least. We also find a reversible doubling of layer size as temperature is raised from 7.7 to 15°C in the case of triple helical soluble collagen adsorbed end on to glass. 

Presumably, when fat was present it was drawn into the layer between the bubbles and disrupted the protein layers, causing the foam to collapse. 

Information concerning myelin structure is also available from electron microscope studies, which visualize myelin as a series of alternating dark and less dark lines (protein layers) separated by unstained zones (the lipid hydrocarbon chains) (Figs 4-4 to 4-7). There is asymmetry in the staining of the protein layers. The less dark, or intraperiod, line represents the closely apposed outer protein... 

Guided mode calculations were also carried out to compare the sensor response of several waveguide systems. In these simulations a model molecular monolayer is represented by a 2-nm thick layer with a refractive index of n 1.5. The optical properties of this model layer are typical of a dense layer of organic molecules on a substrate1 41, and are a reasonable approximation for a streptavidin protein layer bound to a biotinylated surface, the experimental model system we use to characterize our sensors. The ambient upper cladding was assumed to be water with a refractive index of n 1.32. For all examples, the lower cladding was assumed to be Si02 with an index of n 1.44. In the simulations, the effective index of... 

If the height fluctuations for a specified laser beam area a are uncorrelated and characterized by a standard deviation Aha, then the standard error on N measurements of spot height is simply / mln = Ah, j /N. To express this in terms of the total scanned area A of a protein layer, it becomes... 

V. Hlady, D. R. Reinecke, and J. D. Andrade, Fluorescence of adsorbed protein layers ... 

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