Protein Passivation

In the mid to late 60 s, considerable interest in the pre-adsorption of proteins evolved. The basic idea was that if one could saturate the surface with a layer of proteins, then the surface would not be available for the binding and activation of Hageman Factor 

The result was that albumin passivation came into vogue for sometime. In fact, artificial kidneys and blood oxygenators were often treated with albumin solutions prior to clinical use 118,119). There is considerable evidence that such pre-treatment did indeed result in decreased platelet adhesion and activation for short periods, perhaps up to several hours, but that the effect was relatively short-lived. 

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Reverse stains In 1974, Wallace et al. developed reverse staining just to improve recovery of proteins for subsequent microchemical characterization. However, reverse stains are not suitable for quantitative analysis and staining of transfer membranes. The procedure is based on detection of proteins as transfer zones on a black background and used for visualization of proteins, passive elution of intact proteins from gels, and analysis by MS. Over the years, several different forms of procedures have been developed for reverse staining (Table 5.2). 

In passive immunotherapy immune globulin (Ig) is an effective replacement in most forms of antibody deficiency (14). In the past, plasma was used instead of immune globulin, but plasma is rarely indicated in the 1990s because of the risk of disease, particularly AIDS, transmission. Because plasma contains many factors in addition to immunoglobulins (Igs), plasma is, however, of particular value in patients with protein-losing enteropathy, complement deficiencies, and refractory diarrhea. 

Materials may be absorbed by a variety of mechanisms. Depending on the nature of the material and the site of absorption, there may be passive diffusion, filtration processes, faciHtated diffusion, active transport and the formation of microvesicles for the cell membrane (pinocytosis) (61). EoUowing absorption, materials are transported in the circulation either free or bound to constituents such as plasma proteins or blood cells. The degree of binding of the absorbed material may influence the availabiHty of the material to tissue, or limit its elimination from the body (excretion). After passing from plasma to tissues, materials may have a variety of effects and fates, including no effect on the tissue, production of injury, biochemical conversion (metaboli2ed or biotransformed), or excretion (eg, from liver and kidney). 

Proteins are usually separated into two distinct functional classes passive structural materials, which are built up from long fibers, and active components of cellular machinery in which the protein chains are arranged in small compact domains, as we have discussed in earlier chapters. In spite of their differences in structure and function, both these classes of proteins contain a helices and/or p sheets separated by regions of irregular structure. In most cases the fibrous proteins contain specific repetitive amino acid sequences that are necessary for their specific three-dimensional structure. 

Proteins that can flip phospholipids from one side of a bilayer to the other have also been identified in several tissues (Figure 9.11). Called flippases, these proteins reduce the half-time for phospholipid movement across a membrane from 10 days or more to a few minutes or less. Some of these systems may operate passively, with no required input of energy, but passive transport alone cannot establish or maintain asymmetric transverse lipid distributions. However, rapid phospholipid movement from one monolayer to the other occurs in an ATP-dependent manner in erythrocytes. Energy-dependent lipid flippase activity may be responsible for the creation and maintenance of transverse lipid asymmetries. 

FIGURE 17.21 A drawing of the arrangement of the elastic protein titin in the skeletal mnscle sarcomere. Titin filaments originate at the periphery of the M band and extend along the myosin filaments to the Z lines. These titin filaments produce the passive tension existing in myofibrils that have been stretched so that the thick and thin filaments no longer overlap and cannot interact. (Adapted from Ohtsuki, ., Maruyama, K, and Ebashi,. S ., 1986. Advances ia Protein Chemisti y 38 1—67.)... 

The qualitative thermodynamic explanation of the shielding effect produced by the bound neutral water-soluble polymers was summarized by Andrade et al. [2] who studied the interaction of blood with polyethylene oxide (PEO) attached to the surfaces of solids. According to their concept, one possible component of the passivity may be the low interfacial free energy (ysl) of water-soluble polymers and their gels. As estimated by Matsunaga and Ikada [3], it is 3.7 and 3.1 mJ/m2 for cellulose and polyvinylalcohol whereas 52.6 and 41.9 mJ/m2 for polyethylene and Nylon 11, respectively. Ikada et al. [4] also found that adsorption of serum albumin increases dramatically with the increase of interfacial free energy of the polymer contacting the protein solution. 

Chloride channels are membrane proteins that allow for the passive flow of anions across biological membranes. As chloride is the most abundant anion under physiological conditions, these channels are often called chloride channels instead of anion channels, even though other anions (such as iodide or nitrate) may permeate better. As some CLC proteins function as CF-channels, whereas other perform CF/H+-exchangers are also mentioned here. 

MTs extend from the centrosome throughout the cytoplasm to the plasma membrane, where they are stabilized by caps. Sliding along the MTs, kinesin and dynein motors transport their cargoes between the center and the periphery of the cell. MTs present in the axons of neur ons are extended not only by addition of heterodimers to the plus ends but also by use of short MTs that initiate in the centrosome. Their axonal transport is mediated by dynein motors that are passively moved along actin filaments. Once formed in the axon, MTs serve as tracks for the fast axonal transport, i.e. the movement of membranous organelles and membrane proteins to the nerve ending. 

Uptake of LCFAs across the lipid-bilayer of most mammalian cells occurs through both a passive diffusion of LCFAs and a protein-mediated LCFA uptake mechanism. At physiological LCFA concentrations (7.5 nM) the protein-mediated, saturable, substrate-specific, and hormonally regulated mechanism of fatty acids accounts for the majority (>90%) of fatty acid uptake by tissues with high LCFA metabolism and storage such as skeletal muscle, adipose tissue, liver,... 

Figure 2. (1) Neutrophils circulating passively in blood capillary. (2) Chemoattractants may be detected by the circulating neutrophils, by the endothelial cells lining the lumen, or both in order that the neutrophils become adhesive. This adhesion is mediated by selectins, a group of cell surface proteins. Neutrophils roll on the surface of the endothelial cells and then actively locomote seeking out spaces between the endothelial cells. (3) The adhesive neutrophils begin to squeeze between endothelial cells. (4) Cells move through the extracellular matrix towards the site of infection. Here adhesion is low and may not be necessary for locomotion. (5) At the site of infection, neutrophils become trapped by increased adhesion where they phagocytose bacteria and liberate the contents of their granules. After Lackie (1982,1986).

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