Protein diffusivity

Boyer, PM Hsu, JT, Experimental Studies of Restricted Protein Diffusion in an Agarose Matrix, AIChE Journal 38, 259, 1992. 

SJ Gibbs, EN Lightfoot, TW Root. Protein diffusion in porous gel filtration chromatography media studied by pulsed field gradient NMR spectroscopy. J Phys Chem 96 7458-7462, 1992. 

The adsorption of GFP molecules on mesoporous silicas takes place in three fundamental steps. First, the protein molecules in the bulk phase are transported close to the silica, either by convection or diffusion. Second, the protein is adsorbed on the surface of the silicas by electrostatic and Coulomb interactions which are mostly the dominant forces to be at stake. Third, the adsorbed proteins diffuse into the inner of pores and channels. 

Kofinas et al. (1996) have prepared PEO hydrogels by a similar technique. In this work, they studied the diffusional behavior of two macromolecules, cytochrome C and hemoglobin, in these gels. They noted an interesting, yet previously unreported dependence between the crosslink density and protein diffusion coefficient and the initial molecular weight of the linear PEGs. 

The fluidity of lipid bilayers permits dynamic interactions among membrane proteins. For example, the interactions of a neurotransmitter or hormone with its receptor can dissociate a transducer protein, which in turn will diffuse to interact with other effector proteins (Ch. 19). A given effector protein, such as adenylyl cyclase, may respond differently to different receptors because of mediation by different transducers. These dynamic interactions require rapid protein diffusion within the plane of the membrane bilayer. Receptor occupation can initiate extensive redistribution of membrane proteins, as exemplified by the clustering of membrane antigens consequent to binding bivalent antibodies [8]. In contrast to these examples of lateral mobility, the surface distribution of integral membrane proteins can be fixed by interactions with other proteins. Membranes may also be partitioned into local spatial domains consisting of networks... 

Small molecules that act as collisional quenchers may penetrate into the internal structure of proteins, diffuse, and cause quenching upon collision with the aromatic groups. Lakowicz and Weber(53) have shown that the interaction of oxygen molecules with buried tryptophan residues in proteins leads to quenching with unexpectedly high rate constants—from 2 x 109 to 7 x 109 M l s 1. Acrylamide is also capable of quenching the fluorescence of buried tryptophan residues, as was shown for aldolase and ribonuclease 7V(54) A more hydrophobic quencher, trichloroethanol, is a considerably more efficient quencher of internal chromophore groups in proteins.(55)... 

Hormone (H), carried to the target tissue on serum binding proteins, diffuses across the plasma membrane and binds to its specific receptor protein (Rec) in the nucleus. 

Niisslein-Volhard found that this mRNA is translated soon after fertilization, and the Bicoid protein diffuses through... 

In general, a crude or partially purified extract is electrophoresed on a sodium dodecyl sulfate polyacrylamide gel (SDS-PAGE) then the protein band is lightly stained and cut out. In the simplest method, the acrylamide gel band is reduced to a pulp, mixed with Freund s adjuvant, and injected. Unfortunately, this technique is not always successful. Its failure can probably be attributed to factors such as the difficulty of disaggregating the acrylamide, the difficulty with which the protein diffuses from the gel, the presence of SDS in large quantities resulting in extensive tissue and cell damage, and finally, the toxicity of the acrylamide... 

The diffusion constant D is a function of both molecular weight and shape. It can be measured by observing the spread of an initially sharp boundary between the protein solution and a solvent as the protein diffuses into the solvent layer. Once we know the value of the diffusion constant, we can combine the information with the sedimentation data and calculate the molecular weight of the protein. 

The pattern-forming process continues on fertilization as the bed mRNA is translated, the protein diffuses from the anterior pole so that it becomes distributed over about half of the length of the egg (see fig. 31.28 ). Simultaneously, nos gene product originally localized at the posterior pole begins to move forward. 

DNA mediated photoelectron transfer reactions have been demonstrated60 . Binding to DNA assists the electron transfer between the metal-centered donor-acceptor pairs. The increase in rate in the presence of DNA illustrates that reactions at a macromolecular surface may be faster than those in bulk homogeneous phase. These systems can provide models for the diffusion of molecules bound on biological macromolecular surfaces, for protein diffusion along DNA helices, and in considering the effect of medium, orientation and diffusion on electron transfer on macromolecular surfaces. 

The solution diffusion properties of FITC-labelled BSA were measured by FRAP [12], The results showed that the protein diffused freely in solution with a diffusion coefficient of approximately 3xl0 7 cm2/s. This was in reasonable agreement with previously published values [36]. FRAP measurements were also made on thin films stabilized by FITC-BSA. The films were allowed to drain to equilibrium thickness before measurements were initiated. Thin films covering a range of different thicknesses were studied by careful adjustment of solution conditions. BSA stabilized films that had thicknesses up to 40 nm showed no evidence of surface diffusion as there was no return of fluorescence after the bleach pulse in the recovery part of the FRAP curve (Figure 14(c)). In contrast, experiments performed with thin films that were > 80 nm thick showed partial recovery (55%) of the prebleach level of fluorescence (Figure 14(b)). This suggested the presence of two classes of protein in the film one fraction in an environment where it was unable to diffuse laterally, as seen with the films of thicknesses < 45 nm, and a second fraction that was able to diffuse with a calculated diffusion coefficient of lxlO 7 cm2/s. This latter diffusion coefficient was 3 times slower than that... 

Nutrient medium is supplemented with 5% fetal bovine serum. Low molecular weight serum proteins diffuse across the dialysis membrane between the nutrient and production modules. A reservoir of low molecular proteins is required in the nutrient module to maintain the equilibrium for hybridoma growth and survival. Accumulation of foam in the nutrient module can be a problem. To counteract foaming, do not exceed a concentration of 5% FBS in the nutrient module and add AntiFOAMa antifoaming agent. Do not fill the nutrient module with more than 400 mL of nutrient medium. An air space is required within the module to ensure successful hybridoma growth. 

Summarizing the considerations on particle side mass transport, slow protein diffusion in porous adsorbents seems to have the same dominant influence on the efficiency of a fluidized bed adsorption as it frequently is the case in a packed bed. Contrary to conventional protein chromatography increasing... 

Bell CL, Peppas NA. Water, solute and protein diffusion in physiologically responsive hydrogels of poly(methacrylic acid-g-ethylene glycol). Biomaterials 1996, 17, 1203-1218. 

Here A//adS is the enthalpy of adsorption, T is the temperature, and AAads is the entropy change associated with the adsorption of the protein onto the surface. Protein adsorption will take place if AGads < 0. Considering a complex system, where proteins are dissolved in an aqueous environment, and are brought into contact with an artificial interface, there are a vast number of parameters that impact AGads due to their small size (i.e., large diffusion coefficient), water molecules are the first to reach the surface when a solid substrate is placed in an aqueous biological environment. Hence, a hydrate layer is formed. With some delay, proteins diffuse to the interface and competition for a suitable spot for adsorption starts. This competition... 

The freshly discharged and swelled mucus is now free to flow and anneal with the extracellular mucus gel. Since the same tracer protein diffuses at least 150-fold faster in the extracellular matrix than in the intragranular mucin matrix (Perez-Vilar et al. 2005a Perez-Vilar, unpublished observations), which has an average pore size of 5-10 nm, the mucus network mesh size might be in the micron range (see Section 2.7). 

Papadopoulos, S., K.D. Jurgens, and G. Gros (2000). Protein diffusion in living skeletal muscle fibers dependence on protein size, fiber type, and contraction. Biophys. J. 79 2084-2094. 

Sectioned portion contains crush artifact caused by grossing tissue with dull scalpel or razor. Serum proteins diffuse through tissue and are fixed in place. Re-cut tissue using sharp blade. 115-121... 

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